CVE-2023-53338: lwt: Fix return values of BPF xmit ops

Severity: high (CVSS 7.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.6% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-09-17 · updated 2026-08-04
Weakness: CWE-416

Description

In the Linux kernel, the following vulnerability has been resolved: lwt: Fix return values of BPF xmit ops BPF encap ops can return different types of positive values, such like NET_RX_DROP, NET_XMIT_CN, NETDEV_TX_BUSY, and so on, from function skb_do_redirect and bpf_lwt_xmit_reroute. At the xmit hook, such return values would be treated implicitly as LWTUNNEL_XMIT_CONTINUE in ip(6)_finish_output2. When this happens, skbs that have been freed would continue to the neighbor subsystem, causing use-after-free bug and kernel crashes. To fix the incorrect behavior, skb_do_redirect return values can be simply discarded, the same as tc-egress behavior. On the other hand, bpf_lwt_xmit_reroute returns useful errors to local senders, e.g. PMTU information. Thus convert its return values to avoid the conflict with LWTUNNEL_XMIT_CONTINUE.

Affected products

Linux kernel: from 4.10 before 5.4.257; from 5.5 before 5.10.195; from 5.11 before 5.15.132; from 5.16 before 6.1.53; from 6.2 before 6.4.16; from 6.5 before 6.5.3 — fixed in 5.10.195, 5.15.132, 5.4.257, 6.1.53, 6.4.16, 6.5.3

How to fix

Upgrade to a fixed version: Linux kernel 5.10.195, 5.15.132, 5.4.257, 6.1.53. Check the vendor advisory for mitigations.

References

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