From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74430][MODERATE 7.0] rxrpc: Fix ACKALL packet handling Date: Sun, 16 Aug 2026 07:17:12 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74430 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 5 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 8db6a2c95e36938076b37466ce36774526a5c8c3 List-Id: CVE: CVE-2026-74430 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: rxrpc: Fix ACKALL packet handling Commit: 8db6a2c95e36938076b37466ce36774526a5c8c3 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8db6a2c95e36938076b37466ce36774526a5c8c3 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74430 Analysis date: Sun, 16 Aug 2026 07:17:12 -0400 ActionableScore: 5 ActionableScore lower bound: unknown Actionable bucket: Actionable Moderate at minimum Manual review required: YES Summary: A forged RXRPC ACKALL packet can be accepted in an invalid call state before transmit buffers exist, causing rxrpc_rotate_tx_window() to dereference a NULL tx_queue and crash the kernel remotely. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74430 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74430 The original announcement does not normally provide a security severity estimate, CVSS assessment, or enough information to determine whether the reported kernel bug represents a practically relevant security issue. This report was generated by AL-KERNEL, an AI-assisted Linux kernel vulnerability analysis system developed by Alexander Larkin. It combines an autonomous classifier with LLM-assisted technical analysis and a separate ActionableScore mechanism. The purpose of this report is to prioritize Linux kernel CVEs before manual review, identify cases that require prompt investigation, and support automatic closure of issues that are unlikely to have meaningful security impact. Published priority for this report: MODERATE 7.0 Manual review required: YES A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-74430 MODERATE CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';**CWE-476;*CWE-20;CWE-754;BEST CVSS score: '7.5';DESCR 'An RXRPC ACKALL handling flaw allows an out of state ACKALL packet to be accepted for a new service call before any reply data has been queued. In RXRPC_CALL_SERVER_RECV_REQUEST, call tx_top can be zero and call tx_queue can be NULL, so processing ACKALL can reach rxrpc_rotate_tx_window and trigger a NULL pointer dereference. For the CVSS the PR:N because a remote peer only needs network reachability to an RXRPC endpoint and does not need local access or authenticated kernel privileges. The issue is network reachable over RXRPC protocol traffic, but practical exposure depends on whether RXRPC or AFS style services are enabled and reachable from untrusted networks. Impact is denial of service via kernel crash. No confidentiality or integrity impact is assigned because the supported primitive is a NULL pointer dereference rather than UAF, OOB access, or arbitrary write.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5) SKIP CVE-2026-74430 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: b341a0263b1b804d329f864c2dc24815364510ec YES NO NO unknown MAYBE DANGER LINUS KPANIC PACKET KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ## 1. ActionableScore * Conservative score: 5 * Paranoid score: 5 * Final recommended bucket: **Actionable Moderate at minimum**:: This is not an Important-class memory corruption candidate because the supported primitive is a NULL pointer dereference, not UAF, OOB write, type confusion, arbitrary write, or reclaimable lifetime corruption. It is still actionable because it is a network-triggerable kernel crash in a protocol receive path. ## 2. Signal breakdown * Remote reachable / network-triggerable: +2 A forged RXRPC ACKALL packet can be sent by a remote peer to a reachable RXRPC endpoint. * Reliable kernel crash / strong DoS: +1 The commit explicitly states that rxrpc_rotate_tx_window() can dereference a NULL txqueue and trigger a NULL pointer dereference. * Availability impact realistic: +1 The described failure is a kernel NULL dereference, so impact is host availability loss rather than only a local process failure. * Networking protocol receive path: +1 The vulnerable path is RXRPC input packet handling, specifically ACKALL processing. Not awarded: * Generic memory corruption: +0 This is a NULL pointer dereference, not a demonstrated UAF, OOB write, double free, or type confusion. * Privilege escalation plausible: +0 No reclaim, overwrite, callback control, stale object reuse, or arbitrary write primitive is shown. * Confidentiality / Integrity: +0 The patch supports DoS only. ## 3. Reachability analysis A remote peer can trigger the bug if it can send RXRPC traffic to an affected endpoint and cause a forged or out-of-state ACKALL packet to be processed for a call that has no queued transmit buffer. No local user account or kernel privileges are required on the victim, so PR:N is appropriate for CVSS-style reasoning. Exposure depends on whether RXRPC/AFS-style services are enabled and reachable. RXRPC is not as broadly exposed as TCP/IP core paths, but when deployed it is a real network protocol input path. Namespaces do not materially reduce the remote-trigger nature if the endpoint is reachable from the attacker. Call-site confidence: high, because the affected handler and the direct NULL dereference path are described in the commit and visible in the patch context. ## 4. Severity interpretation This behaves like an actionable Moderate remote DoS rather than an ordinary low-priority Moderate. The realistic impact is a kernel crash from a crafted protocol packet. The theoretical memory-corruption potential is low. The patch and commit identify a NULL tx_queue dereference, but do not show attacker-controlled reuse, stale object lifetime, writable freed memory, object confusion, or code execution potential. Therefore the score should not be raised into Strong Important solely based on kernel context. ## 5. One-sentence report phrase A forged RXRPC ACKALL packet can be accepted in an invalid call state before transmit buffers exist, causing rxrpc_rotate_tx_window() to dereference a NULL tx_queue and crash the kernel remotely. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: this is network reachable and can cause a remote kernel crash, even though the demonstrated primitive is DoS-only and does not currently support confidentiality, integrity, or privilege-escalation impact. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: rxrpc: Fix ACKALL packet handling Commit: 8db6a2c95e36938076b37466ce36774526a5c8c3 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8db6a2c95e36938076b37466ce36774526a5c8c3 Commit description: 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]. Fixes: b341a02 ("rxrpc: Implement progressive transmission queue struct") Reported-by: Yuan Tan Reported-by: Yifan Wu Reported-by: Juefei Pu Reported-by: Zhengchuan Liang Reported-by: Xin Liu Signed-off-by: Wyatt Feng Co-developed-by: David Howells Signed-off-by: David Howells cc: Ren Wei cc: Marc Dionne cc: linux-afs@lists.infradead.org Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20260616155749.2125907-2-dhowells@redhat.com/ [1] Link: https://lore.kernel.org/r/c0fd4fec-1576-4070-b31e-a37d5506f5ed@auristor.com/ [2] Reviewed-by: Jeffrey Altman Link: https://patch.msgid.link/20260624163819.3017002-2-dhowells@redhat.com Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman Changed files: net/rxrpc/ar-internal.h net/rxrpc/call_event.c net/rxrpc/call_object.c net/rxrpc/conn_client.c net/rxrpc/input.c net/rxrpc/sendmsg.c Diff excerpt: Not included in this email. See the upstream URL for the full patch. Full patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8db6a2c95e36938076b37466ce36774526a5c8c3 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74430 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74430 The original CVE announcement normally does not include a security-level estimate. In particular, it may not contain a CVSS assessment, an impact level, or enough information to determine whether the reported bug is a practically relevant security issue. One purpose of this parallel CVE list is to provide that missing technical and prioritization information. The original goal of the AL-KERNEL project was to prioritize Linux kernel CVE analysis automatically before manual review. The system can also help identify non-security issues that may be suitable for automatic closure. This report was generated by AL-KERNEL, an AI-assisted Linux kernel vulnerability analysis system developed by Alexander Larkin. The first analysis stage combines an autonomous classifier with additional LLM-based analysis. The autonomous classifier runs locally on a CPU and is based on a backpropagation neural network. Together, these mechanisms produce a technical vulnerability description, identify likely weakness types, estimate CVSS severity, and provide input for ActionableScore. Two CVSS estimates are retained because incomplete kernel vulnerability information often permits more than one defensible interpretation: Conservative CVSS vector: Not available The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 7.5 The conservative vector represents a lower-impact interpretation. The Best/paranoid vector intentionally represents a plausible upper-bound interpretation and should not automatically be treated as demonstrated real-world impact. CVSS may also need to be adjusted for a particular Linux deployment, because actual reachability, privileges, enabled kernel configuration, hardware, namespaces, exposed device nodes, and other environmental conditions can differ significantly between systems. A separate ActionableScore mechanism evaluates practical remediation urgency. Its analysis may include reachability, attack prerequisites, subsystem exposure, memory-corruption characteristics, denial-of-service reliability, and possible confidentiality, integrity, or privilege-escalation impact. Conservative ActionableScore: unknown Paranoid ActionableScore: 5 The final base severity is taken directly from the second tab-separated field of the AL-KERNEL classification result. ActionableScore does not replace or independently override that final AL-KERNEL decision, and if ActionableScore adjusted impact level of ALKERNEL, then you would see self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7. For an AL-KERNEL result of MODERATE, this report uses the following additional presentation split: ActionableScore below 5 -> MODERATE REGULAR ActionableScore 5 or more -> MODERATE 7.0 The distinction between MODERATE REGULAR and MODERATE 7.0 makes it possible to identify Moderate issues that should receive manual analysis and fixes before lower-priority MODERATE REGULAR issues. In many cases, MODERATE REGULAR fixes may wait for a later rebase or routine update. There is one override in which MODERATE REGULAR becomes MODERATE 7.0 even when the ActionableScore is below 5. When the AL-KERNEL result contains the KPANIC flag, a MODERATE result is always presented as MODERATE 7.0. The KPANIC flag selected with few regexps without usage of AI at all, so it helps to detect cases when Kernel Crash happens and similar (to filter False-Negative results from the LLM usage). KPANIC indicates that a reliable kernel crash, kernel panic, or similarly serious kernel availability impact was identified by the classification workflow. AL-KERNEL base severity for this report: MODERATE KPANIC detected for this report: YES Published priority for this report (same as in Subject): MODERATE 7.0 These results are intended to support engineering triage. They are machine-generated estimates, and cases marked for manual review should be validated by a human security engineer before final disposition. For more info read docs linked from here: https://kernelcve.org/ (and you can submit you own patch there to generate such a report for non-existant CVE-id yet). Note that in many cases this AI tool selects higher severity, than real is (means you can expect Importants instead of Moderate 7.0 or Moderates 7.0 instead of regular Moderates). If you see such cases, please use reply email interface to add additional manual analyses info to this particular CVE. And please, please, let me know when you see Lows instead of Importants or Important instead of Low (because particular for such cases I need to tune this AI tool to make it better for this one and next similar). My contact email for such notifications is alexanjelausa@gmail.com (and both send reply to CVE record itself too and see "reply" button below for howto reply).