---
cve: "CVE-2026-89550"
severity: "CRITICAL"
cvss: 9.8
epss: "0.5%"
vendor: "Linux"
kev: false
exploited: false
published: "2026-09-11 20:19:38"
tags: [cve, security, critical]
source: tsecurity.de CVE-Dossier
exported: "2026-09-24T11:21:15+02:00"
---

# CVE-2026-89550

> 9.8 CRITICAL

## Beschreibung

In the Linux kernel, the following vulnerability has been resolved:

SUNRPC: svcauth_gss: enforce krb5 token minimum length

svcauth_gss_unwrap_priv() validates only an upper bound on the
wire-supplied opaque length before handing the buffer to
gss_unwrap():

    if (len > xdr_stream_remaining(xdr))
            goto unwrap_failed;
    offset = xdr_stream_pos(xdr);
    ...
    maj_stat = gss_unwrap(ctx, offset, offset + len, buf);

The wire value `len` flows unchanged as the upper bound into the
krb5 unwrap path, so a len in [0, 16] passes this check and is
handed to gss_unwrap(). For a krb5 v2 context that lands in
gss_krb5_unwrap_v2(), which reads the 16-byte RFC 4121 token
header fields at ptr+4 and ptr+6 and then calls rotate_left()
before any integrity check. With a sub-header length the header
reads run past the token, and _rotate_left()'s `shift %= buf->len`
path can divide by zero when buf->len has been driven to zero by
the truncated token. A header-only token (len == 16) is equally
invalid: with a non-zero RRC field and the opaque blob ending at
the XDR buffer boundary, rotate_left() builds a zero-length
subbuffer, reaching the same division.

Reject the token at the server entry point before it reaches the
krb5 unwrap core. A valid sealed RFC 4121 token must contain
the 16-byte header plus at least some encrypted payload.

Fix by adding a minimum-length check immediately after the
existing upper-bound check:

    if (len

## 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 ≥ 6.6.157
- Kernel ≥ 6.12.109
- Kernel ≥ 6.18.50
- Kernel ≥ 7.2.4

## Referenzen

- <https://git.kernel.org/stable/c/0ea5b0c7f212c2772d32c2b88287b89a9cdf6edd>
- <https://git.kernel.org/stable/c/dd6afc6cab8c5d387d1ed2f069562ef7bdadd651>
- <https://git.kernel.org/stable/c/de942dd8c2c8358bcad04ce44271954c48924423>
- <https://git.kernel.org/stable/c/2eed1e6a976a44015c3ee78841fe336796e2b21c>
- <https://git.kernel.org/stable/c/a919c5c88769cf8fb3ec071e6078d830bf512489>

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/cve?cve=CVE-2026-89550) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI BITS_