Package: release.debian.org
Severity: normal
Tags: trixie security
X-Debbugs-Cc: [email protected]
Control: affects -1 + src:libcap2
User: [email protected]
Usertags: pu
Hi,
please allow this update of libcap2 for trixie.
[ Reason ]
It cherry-picks a single patch from unstable, fixing CVE-2026-4878.
Upstream considered this very hard to exploit, and I agree. The Security
Team agreed that an update in a point release would be sufficient.
[ Impact ]
Without this, libcap2 in trixie would be left vulnerable.
[ Tests ]
I ran all the autopkgtests, successfully. The reverse dependencies in
unstable, where this has already been fixed, all passed theirs, too.
[ Risks ]
These should be minor, given that it's only a single patch, and the
patch itself is reasonably small.
[ Checklist ]
[x] *all* changes are documented in the d/changelog
[x] I reviewed all changes and I approve them
[x] attach debdiff against the package in (old)stable
[x] the issue is verified as fixed in unstable
[ Changes ]
I only added the cherry-picked patch.
[ Other info ]
None.
Best,
Christian
diff -Nru libcap2-2.75/debian/changelog libcap2-2.75/debian/changelog
--- libcap2-2.75/debian/changelog 2025-07-26 20:46:06.000000000 +0200
+++ libcap2-2.75/debian/changelog 2026-04-06 22:11:41.000000000 +0200
@@ -1,3 +1,9 @@
+libcap2 (1:2.75-10+deb13u1) trixie; urgency=medium
+
+ * Add patch fixing CVE-2026-4878 (TOCTOU race condition)
+
+ -- Christian Kastner <[email protected]> Mon, 06 Apr 2026 22:11:41 +0200
+
libcap2 (1:2.75-10) unstable; urgency=medium
* d/rules: Fix typo in override_dh_auto_clean
diff -Nru
libcap2-2.75/debian/patches/Address-a-potential-TOCTOU-race-condition-in-cap_set_file.patch
libcap2-2.75/debian/patches/Address-a-potential-TOCTOU-race-condition-in-cap_set_file.patch
---
libcap2-2.75/debian/patches/Address-a-potential-TOCTOU-race-condition-in-cap_set_file.patch
1970-01-01 01:00:00.000000000 +0100
+++
libcap2-2.75/debian/patches/Address-a-potential-TOCTOU-race-condition-in-cap_set_file.patch
2026-04-06 22:11:41.000000000 +0200
@@ -0,0 +1,155 @@
+From: "Andrew G. Morgan" <[email protected]>
+Date: Thu, 12 Mar 2026 07:38:05 -0700
+Subject: Address a potential TOCTOU race condition in cap_set_file().
+
+This issue was researched and reported by Ali Raza (@locus-x64). It
+has been assigned CVE-2026-4878.
+
+The finding is that while cap_set_file() checks if a file is a regular
+file before applying or removing a capability attribute, a small
+window existed after that check when the filepath could be overwritten
+either with new content or a symlink to some other file. To do this
+would imply that the caller of cap_set_file() was directing it to a
+directory over which a local attacker has write access, and performed
+the operation frequently enough that an attacker had a non-negligible
+chance of exploiting the race condition. The code now locks onto the
+intended file, eliminating the race condition.
+
+Signed-off-by: Andrew G. Morgan <[email protected]>
+---
+ libcap/cap_file.c | 69 ++++++++++++++++++++++++++++++++++++++++++++++--------
+ progs/quicktest.sh | 14 ++++++++++-
+ 2 files changed, 72 insertions(+), 11 deletions(-)
+
+diff --git a/libcap/cap_file.c b/libcap/cap_file.c
+index 0bc07f7..f02bf9f 100644
+--- a/libcap/cap_file.c
++++ b/libcap/cap_file.c
+@@ -8,8 +8,13 @@
+ #define _DEFAULT_SOURCE
+ #endif
+
++#ifndef _GNU_SOURCE
++#define _GNU_SOURCE
++#endif
++
+ #include <sys/types.h>
+ #include <byteswap.h>
++#include <fcntl.h>
+ #include <sys/stat.h>
+ #include <unistd.h>
+
+@@ -322,26 +327,70 @@ int cap_set_file(const char *filename, cap_t cap_d)
+ struct vfs_ns_cap_data rawvfscap;
+ int sizeofcaps;
+ struct stat buf;
++ char fdpath[64];
++ int fd, ret;
++
++ _cap_debug("setting filename capabilities");
++ fd = open(filename, O_RDONLY|O_NOFOLLOW);
++ if (fd >= 0) {
++ ret = cap_set_fd(fd, cap_d);
++ close(fd);
++ return ret;
++ }
+
+- if (lstat(filename, &buf) != 0) {
+- _cap_debug("unable to stat file [%s]", filename);
++ /*
++ * Attempting to set a file capability on a file the process can't
++ * read the content of. This is considered a non-standard use case
++ * and the following (slower) code is complicated because it is
++ * trying to avoid a TOCTOU race condition.
++ */
++
++ fd = open(filename, O_PATH|O_NOFOLLOW);
++ if (fd < 0) {
++ _cap_debug("cannot find file at path [%s]", filename);
++ return -1;
++ }
++ if (fstat(fd, &buf) != 0) {
++ _cap_debug("unable to stat file [%s] descriptor %d",
++ filename, fd);
++ close(fd);
+ return -1;
+ }
+ if (S_ISLNK(buf.st_mode) || !S_ISREG(buf.st_mode)) {
+- _cap_debug("file [%s] is not a regular file", filename);
++ _cap_debug("file [%s] descriptor %d for non-regular file",
++ filename, fd);
++ close(fd);
+ errno = EINVAL;
+ return -1;
+ }
+
+- if (cap_d == NULL) {
+- _cap_debug("removing filename capabilities");
+- return removexattr(filename, XATTR_NAME_CAPS);
++ /*
++ * While the fd remains open, this named file is locked to the
++ * origin regular file. The size of the fdpath variable is
++ * sufficient to support a 160+ bit number.
++ */
++ if (snprintf(fdpath, sizeof(fdpath), "/proc/self/fd/%d", fd)
++ >= sizeof(fdpath)) {
++ _cap_debug("file descriptor too large %d", fd);
++ errno = EINVAL;
++ ret = -1;
++
++ } else if (cap_d == NULL) {
++ _cap_debug("dropping file caps on [%s] via [%s]",
++ filename, fdpath);
++ ret = removexattr(fdpath, XATTR_NAME_CAPS);
++
+ } else if (_fcaps_save(&rawvfscap, cap_d, &sizeofcaps) != 0) {
+- return -1;
+- }
++ _cap_debug("problem converting cap_d to vfscap format");
++ ret = -1;
+
+- _cap_debug("setting filename capabilities");
+- return setxattr(filename, XATTR_NAME_CAPS, &rawvfscap, sizeofcaps, 0);
++ } else {
++ _cap_debug("setting filename capabilities");
++ ret = setxattr(fdpath, XATTR_NAME_CAPS, &rawvfscap,
++ sizeofcaps, 0);
++ }
++ close(fd);
++ return ret;
+ }
+
+ /*
+diff --git a/progs/quicktest.sh b/progs/quicktest.sh
+index e6c48e6..5dc72f9 100755
+--- a/progs/quicktest.sh
++++ b/progs/quicktest.sh
+@@ -148,7 +148,19 @@ pass_capsh --caps="cap_setpcap=p" --inh=cap_chown
--current
+ pass_capsh --strict --caps="cap_chown=p" --inh=cap_chown --current
+
+ # change the way the capability is obtained (make it inheritable)
++chmod 0000 ./privileged
+ ./setcap cap_setuid,cap_setgid=ei ./privileged
++if [ $? -ne 0 ]; then
++ echo "FAILED to set file capability"
++ exit 1
++fi
++chmod 0755 ./privileged
++ln -s privileged unprivileged
++./setcap -r ./unprivileged
++if [ $? -eq 0 ]; then
++ echo "FAILED by removing a capability from a symlinked file"
++ exit 1
++fi
+
+ # Note, the bounding set (edited with --drop) only limits p
+ # capabilities, not i's.
+@@ -246,7 +258,7 @@ EOF
+ pass_capsh --iab='!%cap_chown,^cap_setpcap,cap_setuid'
+ fail_capsh --mode=PURE1E --iab='!%cap_chown,^cap_setuid'
+ fi
+-/bin/rm -f ./privileged
++/bin/rm -f ./privileged ./unprivileged
+
+ echo "testing namespaced file caps"
+
diff -Nru libcap2-2.75/debian/patches/series libcap2-2.75/debian/patches/series
--- libcap2-2.75/debian/patches/series 2025-07-26 20:46:06.000000000 +0200
+++ libcap2-2.75/debian/patches/series 2026-04-06 22:11:41.000000000 +0200
@@ -5,3 +5,4 @@
Add-support-for-some-less-mainstream-architectures.patch
Extend-support-further-to-__m68k__-and-possibly-__sparc__.patch
Be-more-systematic-using-the-kernel-signal-handler-APIs.patch
+Address-a-potential-TOCTOU-race-condition-in-cap_set_file.patch
