[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
01/08: gnu: dbus: Fix CVE-2019-12749.
01/08: gnu: dbus: Fix CVE-2019-12749.
Thu, 20 Jun 2019 17:03:43 -0400 (EDT)
mbakke pushed a commit to branch master
in repository guix.
Author: Marius Bakke <address@hidden>
Date: Sat Jun 15 13:48:46 2019 +0200
gnu: dbus: Fix CVE-2019-12749.
* gnu/packages/patches/dbus-CVE-2019-12749.patch: New file.
* gnu/local.mk (dist_patch_DATA): Adjust accordingly.
* gnu/packages/glib.scm (dbus)[replacement]: New field.
(dbus/fixed): New variable.
gnu/local.mk | 1 +
gnu/packages/glib.scm | 9 ++
gnu/packages/patches/dbus-CVE-2019-12749.patch | 116 +++++++++++++++++++++++++
3 files changed, 126 insertions(+)
diff --git a/gnu/local.mk b/gnu/local.mk
index 336b5c8..649d901 100644
@@ -740,6 +740,7 @@ dist_patch_DATA =
+ %D%/packages/patches/dbus-CVE-2019-12749.patch \
diff --git a/gnu/packages/glib.scm b/gnu/packages/glib.scm
index 7af7c86..d75b963 100644
@@ -80,6 +80,7 @@
+ (replacement dbus/fixed)
@@ -146,6 +147,14 @@ or through unencrypted TCP/IP suitable for use behind a
shared NFS home directories.")
(license license:gpl2+))) ; or Academic Free License
+ (inherit dbus)
+ (source (origin
+ (inherit (package-source dbus))
+ (patches (append (search-patches "dbus-CVE-2019-12749.patch")
+ (origin-patches (package-source dbus))))))))
diff --git a/gnu/packages/patches/dbus-CVE-2019-12749.patch
new file mode 100644
@@ -0,0 +1,116 @@
+From 47b1a4c41004bf494b87370987b222c934b19016 Mon Sep 17 00:00:00 2001
+From: Simon McVittie <address@hidden>
+Date: Thu, 30 May 2019 12:53:03 +0100
+Subject: [PATCH] auth: Reject DBUS_COOKIE_SHA1 for users other than the server
+The DBUS_COOKIE_SHA1 authentication mechanism aims to prove ownership
+of a shared home directory by having the server write a secret "cookie"
+into a .dbus-keyrings subdirectory of the desired identity's home
+directory with 0700 permissions, and having the client prove that it can
+read the cookie. This never actually worked for non-malicious clients in
+the case where server uid != client uid (unless the server and client
+both have privileges, such as Linux CAP_DAC_OVERRIDE or traditional
+Unix uid 0) because an unprivileged server would fail to write out the
+cookie, and an unprivileged client would be unable to read the resulting
+file owned by the server.
+Additionally, since dbus 1.7.10 we have checked that ~/.dbus-keyrings
+is owned by the uid of the server (a side-effect of a check added to
+harden our use of XDG_RUNTIME_DIR), further ruling out successful use
+by a non-malicious client with a uid differing from the server's.
+Joe Vennix of Apple Information Security discovered that the
+implementation of DBUS_COOKIE_SHA1 was susceptible to a symbolic link
+attack: a malicious client with write access to its own home directory
+could manipulate a ~/.dbus-keyrings symlink to cause the DBusServer to
+read and write in unintended locations. In the worst case this could
+result in the DBusServer reusing a cookie that is known to the
+malicious client, and treating that cookie as evidence that a subsequent
+client connection came from an attacker-chosen uid, allowing
+This is mitigated by the fact that by default, the well-known system
+dbus-daemon (since 2003) and the well-known session dbus-daemon (in
+stable releases since dbus 1.10.0 in 2015) only accept the EXTERNAL
+authentication mechanism, and as a result will reject DBUS_COOKIE_SHA1
+at an early stage, before manipulating cookies. As a result, this
+vulnerability only applies to:
+* system or session dbus-daemons with non-standard configuration
+* third-party dbus-daemon invocations such as at-spi2-core (although
+ in practice at-spi2-core also only accepts EXTERNAL by default)
+* third-party uses of DBusServer such as the one in Upstart
+Avoiding symlink attacks in a portable way is difficult, because APIs
+like openat() and Linux /proc/self/fd are not universally available.
+However, because DBUS_COOKIE_SHA1 already doesn't work in practice for
+a non-matching uid, we can solve this vulnerability in an easier way
+without regressions, by rejecting it early (before looking at
+~/.dbus-keyrings) whenever the requested identity doesn't match the
+identity of the process hosting the DBusServer.
+Signed-off-by: Simon McVittie <address@hidden>
+ dbus/dbus-auth.c | 32 ++++++++++++++++++++++++++++++++
+ 1 file changed, 32 insertions(+)
+diff --git a/dbus/dbus-auth.c b/dbus/dbus-auth.c
+index 37d8d4c9..7390a9d5 100644
+@@ -529,6 +529,7 @@ sha1_handle_first_client_response (DBusAuth *auth,
+ DBusString tmp2;
+ dbus_bool_t retval = FALSE;
+ DBusError error = DBUS_ERROR_INIT;
++ DBusCredentials *myself = NULL;
+ _dbus_string_set_length (&auth->challenge, 0);
+@@ -565,6 +566,34 @@ sha1_handle_first_client_response (DBusAuth *auth,
+ return FALSE;
++ myself = _dbus_credentials_new_from_current_process ();
++ if (myself == NULL)
++ goto out;
++ if (!_dbus_credentials_same_user (myself, auth->desired_identity))
++ * DBUS_COOKIE_SHA1 is not suitable for authenticating that the
++ * client is anyone other than the user owning the process
++ * containing the DBusServer: we probably aren't allowed to write
++ * to other users' home directories. Even if we can (for example
++ * uid 0 on traditional Unix or CAP_DAC_OVERRIDE on Linux), we
++ * must not, because the other user controls their home directory,
++ * and could carry out symlink attacks to make us read from or
++ * write to unintended locations. It's difficult to avoid symlink
++ * attacks in a portable way, so we just don't try. This isn't a
++ * regression, because DBUS_COOKIE_SHA1 never worked for other
++ * users anyway.
++ _dbus_verbose ("%s: client tried to authenticate as \"%s\", "
++ "but that doesn't match this process",
++ DBUS_AUTH_NAME (auth),
++ _dbus_string_get_const_data (data));
++ retval = send_rejected (auth);
++ goto out;
+ /* we cache the keyring for speed, so here we drop it if it's the
+ * wrong one. FIXME caching the keyring here is useless since we use
+ * a different DBusAuth for every connection.
+@@ -679,6 +708,9 @@ sha1_handle_first_client_response (DBusAuth *auth,
+ _dbus_string_zero (&tmp2);
+ _dbus_string_free (&tmp2);
++ if (myself != NULL)
++ _dbus_credentials_unref (myself);
+ return retval;
- branch master updated (28618b0 -> 9a2e5fe), guix-commits, 2019/06/20
- 08/08: gnu: ungoogled-chromium: Disable parallel build., guix-commits, 2019/06/20
- 07/08: gnu: samba: Update to 4.10.5 [fixes CVE-2019-12435, CVE-2019-12436]., guix-commits, 2019/06/20
- 05/08: gnu: openh264: Update to 2.0.0., guix-commits, 2019/06/20
- 01/08: gnu: dbus: Fix CVE-2019-12749.,
- 06/08: gnu: ungoogled-chromium: Update to 75.0.3770.100-0.5d8abc3., guix-commits, 2019/06/20
- 02/08: gnu: python-unidecode: Update to 1.1.0., guix-commits, 2019/06/20
- 03/08: gnu: Use HTTPS for sphinx-doc.org., guix-commits, 2019/06/20
- 04/08: gnu: ungoogled-chromium: Install icons., guix-commits, 2019/06/20