From 212700b9d57c6fa6e621cfac52934a6b9331a64b Mon Sep 17 00:00:00 2001 From: Thomas Perale Date: Fri, 17 Apr 2026 11:05:55 +0200 Subject: [PATCH] package/libcap: patch CVE-2026-4878 Fixes the following vulnerability: - CVE-2026-4878: A flaw was found in libcap. A local unprivileged user can exploit a Time-of-check-to-time-of-use (TOCTOU) race condition in the `cap_set_file()` function. This allows an attacker with write access to a parent directory to redirect file capability updates to an attacker-controlled file. By doing so, capabilities can be injected into or stripped from unintended executables, leading to privilege escalation. For more information, see: - https://www.cve.org/CVERecord?id=CVE-2026-4878 - https://security-tracker.debian.org/tracker/CVE-2026-4878 - https://git.kernel.org/pub/scm/libs/libcap/libcap.git/commit/?id=286ace1259992bd0c5d9016715833f2e148ac596 (cherry picked from commit 76e4d8e3dfb2e5353f1473f72860e62b61a953d1) Signed-off-by: Thomas Perale --- ...OCTOU-race-condition-in-cap-set-file.patch | 162 ++++++++++++++++++ package/libcap/libcap.mk | 3 + 2 files changed, 165 insertions(+) create mode 100644 package/libcap/0001-Address-a-potential-TOCTOU-race-condition-in-cap-set-file.patch diff --git a/package/libcap/0001-Address-a-potential-TOCTOU-race-condition-in-cap-set-file.patch b/package/libcap/0001-Address-a-potential-TOCTOU-race-condition-in-cap-set-file.patch new file mode 100644 index 0000000000..7646cac531 --- /dev/null +++ b/package/libcap/0001-Address-a-potential-TOCTOU-race-condition-in-cap-set-file.patch @@ -0,0 +1,162 @@ +From 286ace1259992bd0c5d9016715833f2e148ac596 Mon Sep 17 00:00:00 2001 +From: "Andrew G. Morgan" +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 +CVE: CVE-2026-4878 +Upstream: https://git.kernel.org/pub/scm/libs/libcap/libcap.git/commit/?id=286ace1259992bd0c5d9016715833f2e148ac596 +Signed-off-by: Thomas Perale +--- + 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 + #include ++#include + #include + #include + +@@ -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" + +-- +cgit 1.3-korg + diff --git a/package/libcap/libcap.mk b/package/libcap/libcap.mk index 25b3a46c44..b0ce257a5a 100644 --- a/package/libcap/libcap.mk +++ b/package/libcap/libcap.mk @@ -11,6 +11,9 @@ LIBCAP_LICENSE = GPL-2.0 or BSD-3-Clause LIBCAP_LICENSE_FILES = License LIBCAP_CPE_ID_VALID = YES +# 0001-Address-a-potential-TOCTOU-race-condition-in-cap-set-file.patch +LIBCAP_IGNORE_CVES += CVE-2026-4878 + LIBCAP_DEPENDENCIES = host-gperf LIBCAP_INSTALL_STAGING = YES