CVE-2026-31649net: stmmac: fix integer underflow in chain mode
Updated under an hour ago ()
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No exploitation reported and no EPSS estimate yet.
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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.
- CVSS
- 9.8 CRITICAL (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- Weakness (CWE)
- Not given
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- Linux
- NVD analysis
- Modified
- Record last updated
- Oct 16, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
Linux Linux linux:linux (from the name) | from 286a837217204b1ef105e3a554d0757e4fdfaac1 before 513e06735f5be575b409d195822195348b164e48; 286a837217204b1ef105e3a554d0757e4fdfaac1 builds before 275bdf762e82082f064e60a92448fa2ac43cf95b; from 286a837217204b1ef105e3a554d0757e4fdfaac1 before a2b68a9a476b9544ff31f1fbcd5d80867a8a5e2f; from 286a837217204b1ef105e3a554d0757e4fdfaac1 before b7b8012193fd98236d7ae05d4b553f010a77b2ef; 286a837217204b1ef105e3a554d0757e4fdfaac1 builds before 2c91b39912278d0878f9ba60ba04d2518b18a08d; 286a837217204b1ef105e3a554d0757e4fdfaac1 builds before 6fca757c20396dc2e604dcc61922264e9e3dc803; 286a837217204b1ef105e3a554d0757e4fdfaac1 builds before 10d12b9240ebf96c785f0e2e4228318cd5f3a3eb; 286a837217204b1ef105e3a554d0757e4fdfaac1 builds before 51f4e090b9f87b40c21b6daadb5c06e6c0a07b67 | CNA record |
Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP siemens:simatic_s7_1500_cpu_1518_4_pn_dp_mfp (from the name) | from V3.1.6 | CISA ADP |
Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP siemens:simatic_s7_1500_cpu_1518f_4_pn_dp_mfp (from the name) | from V3.1.6 | CISA ADP |
Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP siemens:siplus_s7_1500_cpu_1518_4_pn_dp_mfp (from the name) | from V3.1.6 | CISA ADP |
linux linux_kernel linux:linux_kernel | from 3.2.1 before 5.10.253; from 5.11 before 5.15.203; from 5.16 before 6.1.169; from 6.2 before 6.6.135; from 6.7 before 6.12.82; from 6.13 before 6.18.23; from 6.19 before 6.19.13; 3.2; and 7 more ranges | NVD |
References
- https://git.kernel.org/stable/c/513e06735f5be575b409d195822195348b164e48patch
- https://git.kernel.org/stable/c/275bdf762e82082f064e60a92448fa2ac43cf95bpatch
- https://git.kernel.org/stable/c/a2b68a9a476b9544ff31f1fbcd5d80867a8a5e2fpatch
- https://git.kernel.org/stable/c/b7b8012193fd98236d7ae05d4b553f010a77b2efpatch
- https://git.kernel.org/stable/c/2c91b39912278d0878f9ba60ba04d2518b18a08dpatch
- https://git.kernel.org/stable/c/6fca757c20396dc2e604dcc61922264e9e3dc803patch
- https://git.kernel.org/stable/c/10d12b9240ebf96c785f0e2e4228318cd5f3a3ebpatch
- https://git.kernel.org/stable/c/51f4e090b9f87b40c21b6daadb5c06e6c0a07b67patch
- 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
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.