---
cve: "CVE-2026-89541"
severity: "CRITICAL"
cvss: 9.8
epss: "55.4%"
vendor: "Linux"
kev: false
exploited: false
published: "2026-09-11 20:19:37"
tags: [cve, security, critical]
source: tsecurity.de CVE-Dossier
exported: "2026-09-16T13:35:10+02:00"
---

# CVE-2026-89541

> 9.8 CRITICAL

## Beschreibung

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").

## CVSS-Vektor

```
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
```

| Metrik | Wert | Bewertung |
|---|---|---|
| AV Angriffsvektor | Netzwerk | bad |
| AC Komplexität | Gering | bad |
| PR Privilegien | Keine | bad |
| UI Interaktion | Keine | bad |
| S Scope | Unverändert | good |
| C Vertraulichkeit | Hoch | bad |
| I Integrität | Hoch | bad |
| A Verfügbarkeit | Hoch | bad |

## Patch verfügbar (OSV)

- Kernel ≥ 5.10.270
- Kernel ≥ 5.15.221
- Kernel ≥ 6.1.188
- Kernel ≥ 6.6.157
- Kernel ≥ 6.12.109
- Kernel ≥ 6.18.50
- Kernel ≥ 7.2.4

## Referenzen

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

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/cve?cve=CVE-2026-89541) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI BITS_