CVE-2024-26752: l2tp: pass correct message length to ip6_append_data

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-04-03 · updated 2026-06-17
Weakness: CWE-131

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.

Affected products

Debian Linux: 10.0
Linux kernel: from 4.19.296 before 4.19.308; from 5.4.258 before 5.4.270; from 5.10.198 before 5.10.211; from 5.15.135 before 5.15.150; from 6.1.57 before 6.1.80; from 6.6 before 6.6.19 — fixed in 4.19.308, 5.10.211, 5.15.150, 5.4.270, 6.1.80, 6.6.19

How to fix

Upgrade to a fixed version: Linux kernel 4.19.308, 5.10.211, 5.15.150, 5.4.270. Check the vendor advisory for mitigations.

References

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