Version in base suite: 2.66-4+deb12u2 Base version: libcap2_2.66-4+deb12u2 Target version: libcap2_2.66-4+deb12u3 Base file: /srv/ftp-master.debian.org/ftp/pool/main/libc/libcap2/libcap2_2.66-4+deb12u2.dsc Target file: /srv/ftp-master.debian.org/policy/pool/main/libc/libcap2/libcap2_2.66-4+deb12u3.dsc changelog | 6 patches/Address-a-potential-TOCTOU-race-condition-in-cap_set_file.patch | 155 ++++++++++ patches/series | 1 3 files changed, 162 insertions(+) dpkg-source: warning: cannot verify inline signature for /srv/release.debian.org/tmp/tmpftjej164/libcap2_2.66-4+deb12u2.dsc: no acceptable signature found dpkg-source: warning: cannot verify inline signature for /srv/release.debian.org/tmp/tmpftjej164/libcap2_2.66-4+deb12u3.dsc: no acceptable signature found diff -Nru libcap2-2.66/debian/changelog libcap2-2.66/debian/changelog --- libcap2-2.66/debian/changelog 2025-05-30 10:13:17.000000000 +0000 +++ libcap2-2.66/debian/changelog 2026-04-06 20:27:39.000000000 +0000 @@ -1,3 +1,9 @@ +libcap2 (1:2.66-4+deb12u3) bookworm; urgency=medium + + * Add patch fixing CVE-2026-4878 (TOCTOU race condition) + + -- Christian Kastner Mon, 06 Apr 2026 22:27:39 +0200 + libcap2 (1:2.66-4+deb12u2) bookworm; urgency=medium [ Aurelien Jarno ] diff -Nru libcap2-2.66/debian/patches/Address-a-potential-TOCTOU-race-condition-in-cap_set_file.patch libcap2-2.66/debian/patches/Address-a-potential-TOCTOU-race-condition-in-cap_set_file.patch --- libcap2-2.66/debian/patches/Address-a-potential-TOCTOU-race-condition-in-cap_set_file.patch 1970-01-01 00:00:00.000000000 +0000 +++ libcap2-2.66/debian/patches/Address-a-potential-TOCTOU-race-condition-in-cap_set_file.patch 2026-04-06 20:27:39.000000000 +0000 @@ -0,0 +1,155 @@ +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 +--- + 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 776b175..0b1d706 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 libcap2-2.66/debian/patches/series libcap2-2.66/debian/patches/series --- libcap2-2.66/debian/patches/series 2025-05-30 10:13:17.000000000 +0000 +++ libcap2-2.66/debian/patches/series 2026-04-06 20:27:39.000000000 +0000 @@ -4,3 +4,4 @@ Large-strings-can-confuse-libcap-s-internal-strdup-code.patch pam_cap-Fix-potential-configuration-parsing-error.patch Add-a-test-for-bad-group-prefix.patch +Address-a-potential-TOCTOU-race-condition-in-cap_set_file.patch