{"id":"CVE-2026-31649","title":"net: stmmac: fix integer underflow in chain mode","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: stmmac: fix integer underflow in chain mode\n\nThe jumbo_frm() chain-mode implementation unconditionally computes\n\n    len = nopaged_len - bmax;\n\nwhere nopaged_len =…","severity":"critical","cvss":9.8,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","cvssSource":"cna","vendor":"Linux","product":"Linux","affected":["Linux >= 286a837217204b1ef105e3a554d0757e4fdfaac1 < 513e06735f5be575b409d195822195348b164e48","Linux >= 286a837217204b1ef105e3a554d0757e4fdfaac1 < 275bdf762e82082f064e60a92448fa2ac43cf95b","Linux >= 286a837217204b1ef105e3a554d0757e4fdfaac1 < a2b68a9a476b9544ff31f1fbcd5d80867a8a5e2f","Linux >= 286a837217204b1ef105e3a554d0757e4fdfaac1 < b7b8012193fd98236d7ae05d4b553f010a77b2ef","Linux >= 286a837217204b1ef105e3a554d0757e4fdfaac1 < 2c91b39912278d0878f9ba60ba04d2518b18a08d","Linux >= 286a837217204b1ef105e3a554d0757e4fdfaac1 < 6fca757c20396dc2e604dcc61922264e9e3dc803","Linux >= 286a837217204b1ef105e3a554d0757e4fdfaac1 < 10d12b9240ebf96c785f0e2e4228318cd5f3a3eb","Linux >= 286a837217204b1ef105e3a554d0757e4fdfaac1 < 51f4e090b9f87b40c21b6daadb5c06e6c0a07b67","Linux 3.2"],"published":"2026-04-24","updated":"2026-09-08","sourceUpdated":"2026-09-08T08:47:51.175Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-31649","references":[{"url":"https://git.kernel.org/stable/c/513e06735f5be575b409d195822195348b164e48"},{"url":"https://git.kernel.org/stable/c/275bdf762e82082f064e60a92448fa2ac43cf95b"},{"url":"https://git.kernel.org/stable/c/a2b68a9a476b9544ff31f1fbcd5d80867a8a5e2f"},{"url":"https://git.kernel.org/stable/c/b7b8012193fd98236d7ae05d4b553f010a77b2ef"},{"url":"https://git.kernel.org/stable/c/2c91b39912278d0878f9ba60ba04d2518b18a08d"},{"url":"https://git.kernel.org/stable/c/6fca757c20396dc2e604dcc61922264e9e3dc803"},{"url":"https://git.kernel.org/stable/c/10d12b9240ebf96c785f0e2e4228318cd5f3a3eb"},{"url":"https://git.kernel.org/stable/c/51f4e090b9f87b40c21b6daadb5c06e6c0a07b67"}],"tags":["cve.org"],"epss":0.00868,"epssPercentile":0.56961,"ingestedAt":"2026-09-08T15:33:26.990Z","slug":"CVE-2026-31649","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nnet: stmmac: fix integer underflow in chain mode\n\nThe jumbo_frm() chain-mode implementation unconditionally computes\n\n    len = nopaged_len - bmax;\n\nwhere nopaged_len = skb_headlen(skb) (linear bytes only) and bmax is\nBUF_SIZE_8KiB or BUF_SIZE_2KiB.  However, the caller stmmac_xmit()\ndecides to invoke jumbo_frm() based on skb->len (total length including\npage fragments):\n\n    is_jumbo = stmmac_is_jumbo_frm(priv, skb->len, enh_desc);\n\nWhen a packet has a small linear portion (nopaged_len <= bmax) but a\nlarge total length due to page fragments (skb->len > bmax), the\nsubtraction wraps as an unsigned integer, producing a huge len value\n(~0xFFFFxxxx).  This causes the while (len != 0) loop to execute\nhundreds of thousands of iterations, passing skb->data + bmax * i\npointers far beyond the skb buffer to dma_map_single().  On IOMMU-less\nSoCs (the typical deployment for stmmac), this maps arbitrary kernel\nmemory to the DMA engine, constituting a kernel memory disclosure and\npotential memory corruption from hardware.\n\nFix this by introducing a buf_len local variable clamped to\nmin(nopaged_len, bmax).  Computing len = nopaged_len - buf_len is then\nalways safe: it is zero when the linear portion fits within a single\ndescriptor, causing the while (len != 0) loop to be skipped naturally,\nand the fragment loop in stmmac_xmit() handles page fragments afterward.\n\n## Affected\n\n- `Linux >= 286a837217204b1ef105e3a554d0757e4fdfaac1 < 513e06735f5be575b409d195822195348b164e48`\n- `Linux >= 286a837217204b1ef105e3a554d0757e4fdfaac1 < 275bdf762e82082f064e60a92448fa2ac43cf95b`\n- `Linux >= 286a837217204b1ef105e3a554d0757e4fdfaac1 < a2b68a9a476b9544ff31f1fbcd5d80867a8a5e2f`\n- `Linux >= 286a837217204b1ef105e3a554d0757e4fdfaac1 < b7b8012193fd98236d7ae05d4b553f010a77b2ef`\n- `Linux >= 286a837217204b1ef105e3a554d0757e4fdfaac1 < 2c91b39912278d0878f9ba60ba04d2518b18a08d`\n- `Linux >= 286a837217204b1ef105e3a554d0757e4fdfaac1 < 6fca757c20396dc2e604dcc61922264e9e3dc803`\n- `Linux >= 286a837217204b1ef105e3a554d0757e4fdfaac1 < 10d12b9240ebf96c785f0e2e4228318cd5f3a3eb`\n- `Linux >= 286a837217204b1ef105e3a554d0757e4fdfaac1 < 51f4e090b9f87b40c21b6daadb5c06e6c0a07b67`\n- `Linux 3.2`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"midnight","depthScore":54,"depthScoreParts":{"impact":53.9,"likelihood":0.2,"exploitation":0,"ransomware":0},"changes":[]}