---
cve: "CVE-2026-31649"
severity: "CRITICAL"
cvss: 9.8
epss: "46%"
vendor: "Linux"
kev: false
exploited: false
published: "2026-04-24 15:16:44"
tags: [cve, security, critical]
source: tsecurity.de CVE-Dossier
exported: "2026-09-18T05:11:40+02:00"
---

# CVE-2026-31649

> 9.8 CRITICAL

## Beschreibung

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

net: stmmac: fix integer underflow in chain mode

The jumbo_frm() chain-mode implementation unconditionally computes

    len = nopaged_len - bmax;

where nopaged_len = skb_headlen(skb) (linear bytes only) and bmax is
BUF_SIZE_8KiB or BUF_SIZE_2KiB.  However, the caller stmmac_xmit()
decides to invoke jumbo_frm() based on skb->len (total length including
page fragments):

    is_jumbo = stmmac_is_jumbo_frm(priv, skb->len, enh_desc);

When a packet has a small linear portion (nopaged_len len > bmax), the
subtraction wraps as an unsigned integer, producing a huge len value
(~0xFFFFxxxx).  This causes the while (len != 0) loop to execute
hundreds of thousands of iterations, passing skb->data + bmax * i
pointers far beyond the skb buffer to dma_map_single().  On IOMMU-less
SoCs (the typical deployment for stmmac), this maps arbitrary kernel
memory to the DMA engine, constituting a kernel memory disclosure and
potential memory corruption from hardware.

Fix this by introducing a buf_len local variable clamped to
min(nopaged_len, bmax).  Computing len = nopaged_len - buf_len is then
always safe: it is zero when the linear portion fits within a single
descriptor, causing the while (len != 0) loop to be skipped naturally,
and the fragment loop in stmmac_xmit() handles page fragments afterward.

## 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 ≥ 5.10.253
- Kernel ≥ 5.15.203
- Kernel ≥ 6.1.169
- Kernel ≥ 6.6.135
- Kernel ≥ 6.12.82
- Kernel ≥ 6.18.23
- Kernel ≥ 6.19.13

## Referenzen

- <https://git.kernel.org/stable/c/513e06735f5be575b409d195822195348b164e48>
- <https://git.kernel.org/stable/c/275bdf762e82082f064e60a92448fa2ac43cf95b>
- <https://git.kernel.org/stable/c/a2b68a9a476b9544ff31f1fbcd5d80867a8a5e2f>
- <https://git.kernel.org/stable/c/b7b8012193fd98236d7ae05d4b553f010a77b2ef>
- <https://git.kernel.org/stable/c/2c91b39912278d0878f9ba60ba04d2518b18a08d>
- <https://git.kernel.org/stable/c/6fca757c20396dc2e604dcc61922264e9e3dc803>
- <https://git.kernel.org/stable/c/10d12b9240ebf96c785f0e2e4228318cd5f3a3eb>
- <https://git.kernel.org/stable/c/51f4e090b9f87b40c21b6daadb5c06e6c0a07b67>
- <https://cert-portal.siemens.com/productcert/html/ssa-019113.html>
- <https://cert-portal.siemens.com/productcert/html/ssa-082556.html>

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/cve?cve=CVE-2026-31649) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI BITS_