CVE-2026-74691
CVE-2026-74691 is a security vulnerability in Kernel. O3 Security confirms whether CVE-2026-74691 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
net: thunderbolt: Tear down DMA paths before stopping the rings
Real-World Exposure
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Description
In the Linux kernel, the following vulnerability has been resolved:
net: thunderbolt: Tear down DMA paths before stopping the rings
tbnet_tear_down() stops both rings and frees their frame buffers before calling tb_xdomain_disable_paths(). tb_ring_stop() zeroes the ring's descriptor base and tbnet_free_buffers() unmaps and frees the pages the frames sit in, so by the time __tb_path_deactivate_hop() polls the hop's 'pending' bit, anything still in flight has nowhere to drain to.
The teardown sequence has been in this order since the driver was added. The setup path has not: commit ff7cd07f3064 ("net: thunderbolt: Enable DMA paths only after rings are enabled") moved the path enable to the end of tbnet_connected_work() and documented why:
/* Both logins successful so enable the rings, high-speed DMA
* paths and start the network device queue.
*
* Note we enable the DMA paths last to make sure we have primed
* the Rx ring before any incoming packets are allowed to
* arrive.
*/
Teardown was never updated to match, so the rings and the paths now come down in the same order they go up instead of in reverse.
On an ASMedia ASM4242 host router the 'pending' bit then never clears: every teardown burns the full 500 ms timeout and __tb_path_deactivate_hop() returns -ETIMEDOUT. Raising the timeout to 5 s does not help, so the hop is not slow to drain, it never drains at all.
The failure is invisible above the thunderbolt core. __tb_path_deactivate_hops() is void and only calls tb_port_warn(); tb_path_deactivate(), tb_tunnel_deactivate() and __tb_disconnect_xdomain_paths() are void as well, and tb_disconnect_xdomain_paths() ends in an unconditional "return 0". So tb_xdomain_disable_paths() reports success and the netdev_warn() below it never fires. Repeated teardowns eventually take the XDomain control channel down, after which the peer node is gone and only a power cycle brings the controller back.
Deactivating the paths first fixes it. Measured with kretprobes on a stock v6.17 tree with no other patches applied, on a link that was up and had just carried traffic:
before: __tb_path_deactivate_hop() returns 0 for the first hop, then -ETIMEDOUT for the second 500335 us later after: 0 for both, 525 us apart
Alternating the two orderings ABBA over three load levels, four teardowns per arm: every teardown failed before the change (21 of 21 that ran), none failed after (0 of 24). The before arms ran short because the link died partway through. The same split shows up when the interface is enslaved to a bond instead of just brought down, which is how I ran into this in the first place. Throughput and latency after the change are unchanged.
Hosts whose routers drain the hop despite the stale descriptor base see no functional difference, since the paths end up deactivated either way.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐧Linux | Kernel | ≥ 4.15.0&&< 5.15.216 | 5.15.216 |
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 5.15.216 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-74691 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-2026-74691 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-2026-74691. 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-2026-74691 in your dependencies?
O3 detects CVE-2026-74691 across Linux dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.