CVE-2026-23394

Description

In the Linux kernel, the following vulnerability has been resolved: af_unix: Give up GC if MSG_PEEK intervened. Igor Ushakov reported that GC purged the receive queue of an alive socket due to a race with MSG_PEEK with a nice repro. This is the exact same issue previously fixed by commit cbcf01128d0a ("af_unix: fix garbage collect vs MSG_PEEK"). After GC was replaced with the current algorithm, the cited commit removed the locking dance in unix_peek_fds() and reintroduced the same issue. The problem is that MSG_PEEK bumps a file refcount without interacting with GC. Consider an SCC containing sk-A and sk-B, where sk-A is close()d but can be recv()ed via sk-B. The bad thing happens if sk-A is recv()ed with MSG_PEEK from sk-B and sk-B is close()d while GC is checking unix_vertex_dead() for sk-A and sk-B. GC thread User thread --------- ----------- unix_vertex_dead(sk-A) -> true <------. \ `------ recv(sk-B, MSG_PEEK) invalidate !! -> sk-A's file refcount : 1 -> 2 close(sk-B) -> sk-B's file refcount : 2 -> 1 unix_vertex_dead(sk-B) -> true Initially, sk-A's file refcount is 1 by the inflight fd in sk-B recvq. GC thinks sk-A is dead because the file refcount is the same as the number of its inflight fds. However, sk-A's file refcount is bumped silently by MSG_PEEK, which invalidates the previous evaluation. At this moment, sk-B's file refcount is 2; one by the open fd, and one by the inflight fd in sk-A. The subsequent close() releases one refcount by the former. Finally, GC incorrectly concludes that both sk-A and sk-B are dead. One option is to restore the locking dance in unix_peek_fds(), but we can resolve this more elegantly thanks to the new algorithm. The point is that the issue does not occur without the subsequent close() and we actually do not need to synchronise MSG_PEEK with the dead SCC detection. When the issue occurs, close() and GC touch the same file refcount. If GC sees the refcount being decremented by close(), it can just give up garbage-collecting the SCC. Therefore, we only need to signal the race during MSG_PEEK with a proper memory barrier to make it visible to the GC. Let's use seqcount_t to notify GC when MSG_PEEK occurs and let it defer the SCC to the next run. This way no locking is needed on the MSG_PEEK side, and we can avoid imposing a penalty on every MSG_PEEK unnecessarily. Note that we can retry within unix_scc_dead() if MSG_PEEK is detected, but we do not do so to avoid hung task splat from abusive MSG_PEEK calls.

CVSS Details

CVSS Score

4.7

Severity

MEDIUM

CVSS Vector

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H

Configurations (Affected Products)

cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* - VULNERABLE

cpe:2.3:o:linux:linux_kernel:6.10:-:*:*:*:*:*:* - VULNERABLE

Linux Kernel (具体受影响版本请参考厂商公告)

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

#include <stdio.h>
#include <unistd.h>
#include <sys/socket.h>

int main() {
    int sv[2];
    socketpair(AF_UNIX, SOCK_DGRAM, 0, sv);
    
    if (fork() == 0) {
        char buf[128];
        // Child: Trigger MSG_PEEK race
        while(1) recv(sv[1], buf, sizeof(buf), MSG_PEEK);
    } else {
        // Parent: Close socket to trigger GC logic
        sleep(1);
        close(sv[0]);
        close(sv[1]);
        wait(NULL);
    }
    return 0;
}

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-23394
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-23394
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-23394/
[4] VulDB https://vuldb.com/cve/CVE-2026-23394
[5] https://git.kernel.org/stable/c/37dd7ab332396eb8dd80b2dc7ea4b61abf767436
[6] https://git.kernel.org/stable/c/72cf49ad50c16270b52bc512d9c2df5743922968
[7] https://git.kernel.org/stable/c/e5b31d988a41549037b8d8721a3c3cae893d8670

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-23394", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-03-25T11:16:40.190", "lastModified": "2026-04-24T15:20:29.353", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\naf_unix: Give up GC if MSG_PEEK intervened.\n\nIgor Ushakov reported that GC purged the receive queue of\nan alive socket due to a race with MSG_PEEK with a nice repro.\n\nThis is the exact same issue previously fixed by commit\ncbcf01128d0a (\"af_unix: fix garbage collect vs MSG_PEEK\").\n\nAfter GC was replaced with the current algorithm, the cited\ncommit removed the locking dance in unix_peek_fds() and\nreintroduced the same issue.\n\nThe problem is that MSG_PEEK bumps a file refcount without\ninteracting with GC.\n\nConsider an SCC containing sk-A and sk-B, where sk-A is\nclose()d but can be recv()ed via sk-B.\n\nThe bad thing happens if sk-A is recv()ed with MSG_PEEK from\nsk-B and sk-B is close()d while GC is checking unix_vertex_dead()\nfor sk-A and sk-B.\n\n  GC thread                    User thread\n  ---------                    -----------\n  unix_vertex_dead(sk-A)\n  -> true   <------.\n                    \\\n                     `------   recv(sk-B, MSG_PEEK)\n              invalidate !!    -> sk-A's file refcount : 1 -> 2\n\n                               close(sk-B)\n                               -> sk-B's file refcount : 2 -> 1\n  unix_vertex_dead(sk-B)\n  -> true\n\nInitially, sk-A's file refcount is 1 by the inflight fd in sk-B\nrecvq.  GC thinks sk-A is dead because the file refcount is the\nsame as the number of its inflight fds.\n\nHowever, sk-A's file refcount is bumped silently by MSG_PEEK,\nwhich invalidates the previous evaluation.\n\nAt this moment, sk-B's file refcount is 2; one by the open fd,\nand one by the inflight fd in sk-A.  The subsequent close()\nreleases one refcount by the former.\n\nFinally, GC incorrectly concludes that both sk-A and sk-B are dead.\n\nOne option is to restore the locking dance in unix_peek_fds(),\nbut we can resolve this more elegantly thanks to the new algorithm.\n\nThe point is that the issue does not occur without the subsequent\nclose() and we actually do not need to synchronise MSG_PEEK with\nthe dead SCC detection.\n\nWhen the issue occurs, close() and GC touch the same file refcount.\nIf GC sees the refcount being decremented by close(), it can just\ngive up garbage-collecting the SCC.\n\nTherefore, we only need to signal the race during MSG_PEEK with\na proper memory barrier to make it visible to the GC.\n\nLet's use seqcount_t to notify GC when MSG_PEEK occurs and let\nit defer the SCC to the next run.\n\nThis way no locking is needed on the MSG_PEEK side, and we can\navoid imposing a penalty on every MSG_PEEK unnecessarily.\n\nNote that we can retry within unix_scc_dead() if MSG_PEEK is\ndetected, but we do not do so to avoid hung task splat from\nabusive MSG_PEEK calls."}, {"lang": "es", "value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\naf_unix: Abandonar la recolección de basura (GC) si MSG_PEEK intervino.\n\nIgor Ushakov informó que la recolección de basura (GC) purgó la cola de recepción de un socket activo debido a una condición de carrera con MSG_PEEK con una buena reproducción.\n\nEste es exactamente el mismo problema previamente solucionado por el commit cbcf01128d0a ('af_unix: corregir recolección de basura vs MSG_PEEK').\n\nDespués de que la recolección de basura (GC) fue reemplazada por el algoritmo actual, el commit citado eliminó la 'danza de bloqueo' en unix_peek_fds() y reintrodujo el mismo problema.\n\nEl problema es que MSG_PEEK incrementa un contador de referencias de archivo sin interactuar con la recolección de basura (GC).\n\nConsidere un SCC que contiene sk-A y sk-B, donde sk-A está close()d (cerrado) pero puede ser recv()ed (recibido) a través de sk-B.\n\nLo malo sucede si sk-A es recv()ed (recibido) con MSG_PEEK desde sk-B y sk-B está close()d (cerrado) mientras la recolección de basura (GC) está verificando unix_vertex_dead() para sk-A y sk-B.\n\n  Hilo de GC                    Hilo de usuario\n  ---------                    -----------\n  unix_vertex_dead(sk-A)\n  -&gt; true   &lt;------.\n                    \\\n                     `------   recv(sk-B, MSG_PEEK)\n              ¡¡invalidar!!    -&gt; contador de referencias de archivo de sk-A : 1 -&gt; 2\n\n                               close(sk-B)\n                               -&gt; contador de referencias de archivo de sk-B : 2 -&gt; 1\n  unix_vertex_dead(sk-B)\n  -&gt; true\n\nInicialmente, el contador de referencias de archivo de sk-A es 1 por el descriptor de archivo en tránsito en la cola de recepción de sk-B. La recolección de basura (GC) piensa que sk-A está muerto porque el contador de referencias de archivo es el mismo que el número de sus descriptores de archivo en tránsito.\n\nSin embargo, el

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