CriticalFix available

net: stmmac: fix integer underflow in chain mode

Type: advisorySources: OSV

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 <= bmax) but a large total length due to page fragments (skb->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.

Products: Kernel
Affected versions: Not specified
Fixed versions: 5.10.253, 5.15.203, 6.1.169, 6.12.82, 6.18.23, 6.19.13, 6.6.135
CVEs: CVE-2026-31649
Confirmed fixed CVEs: Not specified
Updated in this feed: 3 Nov 2026, 16:28 UTC · Revision 1

Source evidence

net: stmmac: fix integer underflow in chain mode

core-osv · Original source

Published 24 Apr 2026, 14:45 UTC

osv:CVE-2026-31649

Kernel

Fixed versions: 5.10.253, 5.15.203, 6.1.169, 6.6.135, 6.12.82, 6.18.23, 6.19.13

Complete source record

{
  "id": "73356b0fc8cc7340ae59efe1abf536cb29a3ef634453279baab52034e612984a",
  "url": "https://osv.dev/vulnerability/CVE-2026-31649",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "net: stmmac: fix integer underflow in chain mode",
    "summary": "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 <= bmax) but a large total length due to page fragments (skb->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.",
    "evidence": "osv:CVE-2026-31649",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
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            "value": "5.10.253",
            "evidence": "/affected/1/ranges"
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          {
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            "evidence": "/affected/1/ranges"
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          {
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            "evidence": "/affected/1/ranges"
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            "evidence": "/affected/1/ranges"
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          {
            "value": "6.12.82",
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          },
          {
            "value": "6.18.23",
            "evidence": "/affected/1/ranges"
          },
          {
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            "evidence": "/affected/1/ranges"
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        "affected_versions": []
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    "severity": "critical",
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      "aliases": [
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      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
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      "affected": [
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                {
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                {
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          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-31649.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "3.2.0"
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                {
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            },
            {
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                {
                  "introduced": "5.11.0"
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            {
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          "package": {
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      ],
      "modified": "2026-10-28T02:30:30.360608021Z",
      "provider": "osv",
      "references": [
        "https://cert-portal.siemens.com/productcert/html/ssa-019113.html",
        "https://cert-portal.siemens.com/productcert/html/ssa-082556.html",
        "https://cert-portal.siemens.com/productcert/html/ssa-457936.html",
        "https://git.kernel.org/stable/c/10d12b9240ebf96c785f0e2e4228318cd5f3a3eb",
        "https://git.kernel.org/stable/c/275bdf762e82082f064e60a92448fa2ac43cf95b",
        "https://git.kernel.org/stable/c/2c91b39912278d0878f9ba60ba04d2518b18a08d",
        "https://git.kernel.org/stable/c/513e06735f5be575b409d195822195348b164e48",
        "https://git.kernel.org/stable/c/51f4e090b9f87b40c21b6daadb5c06e6c0a07b67",
        "https://git.kernel.org/stable/c/6fca757c20396dc2e604dcc61922264e9e3dc803",
        "https://git.kernel.org/stable/c/a2b68a9a476b9544ff31f1fbcd5d80867a8a5e2f",
        "https://git.kernel.org/stable/c/b7b8012193fd98236d7ae05d4b553f010a77b2ef",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31649.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-31649",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31649.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-31649",
        "evidence": "/id"
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    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 497351,
  "published_at": "2026-04-24T14:45:02.52+00:00"
}