CVE-2026-31649Critical· 9.8▾ MidnightIn 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 =…
▾ Midnight zone — Critical, or high with PoC / in-the-wild
impact 53.9 · likelihood 0.1 · exploitation 0
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Stakeholder-Specific Vulnerability Categorization from CISA's ADP record at CVE.org: whether exploitation is observed, whether an attack can be automated, and how much of the system is at stake.
Exploit-prediction probability, daily snapshots since Sep 8.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via NVD
0.5%
0.5% → 0.9%
Last analysed / modified upstream
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.
linux_kernel >= 3.2.1, < 5.10.253linux_kernel >= 5.11, < 5.15.203linux_kernel >= 5.16, < 6.1.169linux_kernel >= 6.2, < 6.6.135linux_kernel >= 6.7, < 6.12.82linux_kernel >= 6.13, < 6.18.23linux_kernel >= 6.19, < 6.19.13linux_kernel = 3.2linux_kernel = 7.0Upgrade past the affected range:
linux_kernel 6.19.13Connected by shared product, vendor, weakness, or advisory.
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