---
cve: "CVE-2026-43233"
severity: "HIGH"
cvss: 8.2
epss: "46%"
vendor: "Linux"
kev: false
exploited: false
published: "2026-05-06 12:16:43"
tags: [cve, security, high]
source: tsecurity.de CVE-Dossier
exported: "2026-09-10T11:37:18+02:00"
---

# CVE-2026-43233

> 8.2 HIGH

## Beschreibung

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

netfilter: nf_conntrack_h323: fix OOB read in decode_choice()

In decode_choice(), the boundary check before get_len() uses the
variable `len`, which is still 0 from its initialization at the top of
the function:

    unsigned int type, ext, len = 0;
    ...
    if (ext || (son->attr & OPEN)) {
        BYTE_ALIGN(bs);
        if (nf_h323_error_boundary(bs, len, 0))  /* len is 0 here */
            return H323_ERROR_BOUND;
        len = get_len(bs);                        /* OOB read */

When the bitstream is exactly consumed (bs->cur == bs->end), the check
nf_h323_error_boundary(bs, 0, 0) evaluates to (bs->cur + 0 > bs->end),
which is false.  The subsequent get_len() call then dereferences
*bs->cur++, reading 1 byte past the end of the buffer.  If that byte
has bit 7 set, get_len() reads a second byte as well.

This can be triggered remotely by sending a crafted Q.931 SETUP message
with a User-User Information Element containing exactly 2 bytes of
PER-encoded data ({0x08, 0x00}) to port 1720 through a firewall with
the nf_conntrack_h323 helper active.  The decoder fully consumes the
PER buffer before reaching this code path, resulting in a 1-2 byte
heap-buffer-overflow read confirmed by AddressSanitizer.

Fix this by checking for 2 bytes (the maximum that get_len() may read)
instead of the uninitialized `len`.  This matches the pattern used at
every other get_len() call site in the same file, where the caller
checks for 2 bytes of available data before calling get_len().

## CVSS-Vektor

```
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/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 | Gering | warn |
| I Integrität | Keine | good |
| A Verfügbarkeit | Hoch | bad |

## Patch verfügbar (OSV)

- Kernel ≥ 5.10.252
- Kernel ≥ 5.15.202
- Kernel ≥ 6.1.165
- Kernel ≥ 6.6.128
- Kernel ≥ 6.12.75
- Kernel ≥ 6.18.16
- Kernel ≥ 6.19.6

## Referenzen

- <https://git.kernel.org/stable/c/bcb50aa0b8f2b74a9fe5a1c7bee6f2657a288041>
- <https://git.kernel.org/stable/c/2a3aac4205e7d2f1aca2e3827de8cdd517d36c4a>
- <https://git.kernel.org/stable/c/81f2fc5b0d0cf4696146f00f837596d10b92dead>
- <https://git.kernel.org/stable/c/7ef82863d42261817a6394c6c881bd6757a70f16>
- <https://git.kernel.org/stable/c/53d32735d77ab56cc3fc7bd53a7d099418f19be1>
- <https://git.kernel.org/stable/c/f0a83d0a4b7c127d32ac06d607a9214937716129>
- <https://git.kernel.org/stable/c/35f1943d242e1b9f0b6e91c0c93bfb293a9f8224>
- <https://git.kernel.org/stable/c/baed0d9ba91d4f390da12d5039128ee897253d60>

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/cve?cve=CVE-2026-43233) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI BITS_