Integer underflow in Linux kernel stmmac jumbo_frm() chain mode
CVE-2026-31649 is an integer underflow vulnerability in the Linux kernel's stmmac network driver, specifically in the jumbo_frm() chain-mode transmit path. The vulnerable code unconditionally computes len = nopaged_len - bmax, where nopaged_len is derived from skb_headlen(skb) and therefore reflects only the linear portion of the socket buffer, while the caller stmmac_xmit() decides whether to invoke jumbo_frm() based on skb->len, which includes page fragments. If a packet's total length exceeds bmax due to fragments but its linear portion is less than or equal to bmax, the subtraction underflows as an unsigned value and produces a very large len. This causes the subsequent while (len != 0) loop to iterate excessively and pass skb->data + bmax * i pointers far beyond the valid skb buffer into dma_map_single(). The fix introduces a local buf_len clamped to min(nopaged_len, bmax), making the subtraction safe and allowing page fragments to be handled later by the fragment loop in stmmac_xmit().
Are you exposed to this one?
Mallory correlates every CVE against your assets, your vendors, and active adversary campaigns. Know which vulnerabilities matter for you, not just which ones are loud.
Impact, mitigation & remediation
What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
Impact
What an attacker gets, and what they’ve been doing with it.
Mitigation
If you can’t patch tonight, do this now.
Remediation
Patch, then assume compromise.
Exploits
No public exploits tracked yet. Mallory keeps watching.
No public exploit code observed for this vulnerability.
Affected products & vendors
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
Recent activity
7 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
The version that knows your environment.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.