CVE-2026-74478
CRITICALCVE-2026-74478 is a critical-severity (CVSS 9.8) vulnerability in Kernel. O3 Security confirms whether CVE-2026-74478 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
um: vector: fix use-after-free in vector_mmsg_rx()
Real-World Exposure
KernelReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Linux packages — download data is not available via public APIs for these ecosystems.
Description
In the Linux kernel, the following vulnerability has been resolved:
um: vector: fix use-after-free in vector_mmsg_rx()
When vector_mmsg_rx() discards a packet whose overlay header fails verify_header(), it frees the skb and continues the loop:
if (header_check < 0) {
dev_kfree_skb_irq(skb);
vp->estats.rx_encaps_errors++;
continue;
}
The normal and short-packet paths fall through to the bottom of the loop body, which clears the consumed slot and advances the cursors:
(*skbuff_vector) = NULL;
mmsg_vector++;
skbuff_vector++;
The verify_header() < 0 path skips that via continue, so the freed skb is left in skbuff_vector[] and the cursors do not advance. The next iteration reads the same slot, gets the freed skb, and frees it again, producing a refcount underflow / use-after-free in the RX path.
Discard the slot the same way the other paths do before continuing.
Only transports whose verify_header() can return negative are affected: GRE and L2TPv3 do so on a cookie/session-id mismatch (raw/tap do not), so any peer on such a transport can trigger it without authentication.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐧Linux | Kernel | ≥ 4.17.0&&< 6.6.151 | 6.6.151 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Kernel. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update Kernel to 6.6.151 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-74478 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-74478 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-74478. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-74478 in your dependencies?
O3 detects CVE-2026-74478 across Linux dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.