CVE-2026-74430
HIGHCVE-2026-74430 is a high-severity (CVSS 7.5) vulnerability in Kernel. O3 Security confirms whether CVE-2026-74430 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
rxrpc: Fix ACKALL packet handling
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:
rxrpc: Fix ACKALL packet handling
rxrpc_input_ackall() accepts ACKALL packets without checking whether the call is in a state that can legitimately have outstanding transmit buffers. A forged ACKALL can therefore reach a new service call in RXRPC_CALL_SERVER_RECV_REQUEST before any reply packets have been queued.
In that state call->tx_top is zero and call->tx_queue is NULL, so rxrpc_rotate_tx_window() dereferences a NULL txqueue and triggers a null-pointer dereference.
Fix the handling of ACKALL packets by the following means:
(1) Add two new call states: RXRPC_CALL_CLIENT_PRE_SEND which indicates that the client call is connected, but nothing has been transmitted as yet; and RXRPC_CALL_CLIENT_AWAIT_ACK, which indicates that everything has been transmitted at least once, but we're now waiting for the stuff remaining in the Tx buffer to be ACK'd (retransmissions may still happen).
The RXRPC_CALL_CLIENT_PRE_SEND state is set when the call is assigned
a channel and transitions to RXRPC_CALL_CLIENT_SEND_REQUEST when the
first packet is transmitted.
RXRPC_CALL_CLIENT_AWAIT_REPLY is then narrowed in scope to indicate
that all Tx packets have been ACK'd and we're now waiting for the
reply to be received.
(2) As per Wyatt Feng's original patch[1], the ACKALL handler then checks that the call state is one in which there might be stuff in the Tx buffer to ACK, but now this includes AWAIT_ACK rather than AWAIT_REPLY. ACKALL packets are ignored if received in the wrong state.
Note that unlike Wyatt Feng's patch, it's no longer necessary to check
to see if the Tx buffer exists as this the state set now covers this.
(3) Make the ACKALL handler use call->tx_transmitted rather than call->tx_top as the former is explicitly the highest packet seq number transmitted, whereas the latter has a looser definition.
Thanks to Jeffrey Altman for a description of the history of the ACKALL packet[1].
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐧Linux | Kernel | ≥ 6.14.0&&< 6.18.40 | 6.18.40 |
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 6.18.40 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-74430 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-2026-74430 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-2026-74430. 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-2026-74430 in your dependencies?
O3 detects CVE-2026-74430 across Linux dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.