FKIE_CVE-2026-31411

Vulnerability from fkie_nvd - Published: 2026-04-08 14:16 - Updated: 2026-05-20 16:03
Severity
5.5 (Medium) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: net: atm: fix crash due to unvalidated vcc pointer in sigd_send() Reproducer available at [1]. The ATM send path (sendmsg -> vcc_sendmsg -> sigd_send) reads the vcc pointer from msg->vcc and uses it directly without any validation. This pointer comes from userspace via sendmsg() and can be arbitrarily forged: int fd = socket(AF_ATMSVC, SOCK_DGRAM, 0); ioctl(fd, ATMSIGD_CTRL); // become ATM signaling daemon struct msghdr msg = { .msg_iov = &iov, ... }; *(unsigned long *)(buf + 4) = 0xdeadbeef; // fake vcc pointer sendmsg(fd, &msg, 0); // kernel dereferences 0xdeadbeef In normal operation, the kernel sends the vcc pointer to the signaling daemon via sigd_enq() when processing operations like connect(), bind(), or listen(). The daemon is expected to return the same pointer when responding. However, a malicious daemon can send arbitrary pointer values. Fix this by introducing find_get_vcc() which validates the pointer by searching through vcc_hash (similar to how sigd_close() iterates over all VCCs), and acquires a reference via sock_hold() if found. Since struct atm_vcc embeds struct sock as its first member, they share the same lifetime. Therefore using sock_hold/sock_put is sufficient to keep the vcc alive while it is being used. Note that there may be a race with sigd_close() which could mark the vcc with various flags (e.g., ATM_VF_RELEASED) after find_get_vcc() returns. However, sock_hold() guarantees the memory remains valid, so this race only affects the logical state, not memory safety. [1]: https://gist.github.com/mrpre/1ba5949c45529c511152e2f4c755b0f3
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/1c8bda3df028d5e54134077dcd09f46ca8cfceb5Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/21c303fec138c002f90ed33bce60e807d53072bbPatch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/3e1a8b00095246a9a2b46b57f6d471c6d3c00ed2Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/440c9a5fc477a8ee259d8bf669531250b8398651Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/69d3f9ee5489e6e8b66defcfa226e91d82393297Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/ae88a5d2f29b69819dc7b04086734439d074a643Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/c96549d07dfdd51aadf0722cfb40711574424840Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/e3f80666c2739296c3b69a127300455c43aa1067Patch
Impacted products
Vendor Product Version
linux linux_kernel *
linux linux_kernel *
linux linux_kernel *
linux linux_kernel *
linux linux_kernel *
linux linux_kernel *
linux linux_kernel *
linux linux_kernel 2.6.12
linux linux_kernel 2.6.12
linux linux_kernel 2.6.12
linux linux_kernel 2.6.12
linux linux_kernel 7.0
linux linux_kernel 7.0
linux linux_kernel 7.0
linux linux_kernel 7.0
linux linux_kernel 7.0
linux linux_kernel 7.0
linux linux_kernel 7.0
To clipboard 

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  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: atm: fix crash due to unvalidated vcc pointer in sigd_send()\n\nReproducer available at [1].\n\nThe ATM send path (sendmsg -\u003e vcc_sendmsg -\u003e sigd_send) reads the vcc\npointer from msg-\u003evcc and uses it directly without any validation. This\npointer comes from userspace via sendmsg() and can be arbitrarily forged:\n\n    int fd = socket(AF_ATMSVC, SOCK_DGRAM, 0);\n    ioctl(fd, ATMSIGD_CTRL);  // become ATM signaling daemon\n    struct msghdr msg = { .msg_iov = \u0026iov, ... };\n    *(unsigned long *)(buf + 4) = 0xdeadbeef;  // fake vcc pointer\n    sendmsg(fd, \u0026msg, 0);  // kernel dereferences 0xdeadbeef\n\nIn normal operation, the kernel sends the vcc pointer to the signaling\ndaemon via sigd_enq() when processing operations like connect(), bind(),\nor listen(). The daemon is expected to return the same pointer when\nresponding. However, a malicious daemon can send arbitrary pointer values.\n\nFix this by introducing find_get_vcc() which validates the pointer by\nsearching through vcc_hash (similar to how sigd_close() iterates over\nall VCCs), and acquires a reference via sock_hold() if found.\n\nSince struct atm_vcc embeds struct sock as its first member, they share\nthe same lifetime. Therefore using sock_hold/sock_put is sufficient to\nkeep the vcc alive while it is being used.\n\nNote that there may be a race with sigd_close() which could mark the vcc\nwith various flags (e.g., ATM_VF_RELEASED) after find_get_vcc() returns.\nHowever, sock_hold() guarantees the memory remains valid, so this race\nonly affects the logical state, not memory safety.\n\n[1]: https://gist.github.com/mrpre/1ba5949c45529c511152e2f4c755b0f3"
    }
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  "id": "CVE-2026-31411",
  "lastModified": "2026-05-20T16:03:38.647",
  "metrics": {
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        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "LOCAL",
          "availabilityImpact": "HIGH",
          "baseScore": 5.5,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "privilegesRequired": "LOW",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
          "version": "3.1"
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        "exploitabilityScore": 1.8,
        "impactScore": 3.6,
        "source": "nvd@nist.gov",
        "type": "Primary"
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  "published": "2026-04-08T14:16:27.977",
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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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