From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-53151][MODERATE REGULAR] rxrpc: Fix the ACK parser to extract the SACK table for parsing Date: Thu, 25 Jun 2026 05:38:37 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-53151 X-AL-KERNEL-Priority: MODERATE REGULAR X-AL-KERNEL-Severity: MODERATE REGULAR X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 4 X-AL-KERNEL-ActionableScore-Lower: 2 X-AL-KERNEL-Commit: 566c4c1244de50fbff1f89ff93c9d7b0fc256db4 List-Id: CVE: CVE-2026-53151 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: rxrpc: Fix the ACK parser to extract the SACK table for parsing Commit: 566c4c1244de50fbff1f89ff93c9d7b0fc256db4 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=566c4c1244de50fbff1f89ff93c9d7b0fc256db4 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53151 Analysis date: Thu, 25 Jun 2026 05:38:37 -0400 ActionableScore: 4 ActionableScore lower bound: 2 Actionable bucket: Borderline, manual review recommended / not auto-close Manual review required: YES Summary: AF_RXRPC ACK parsing may incorrectly read SACK data from a fragmented or non-linear skb after assuming skb_condense made the buffer linear, allowing a remote RXRPC peer in reachable deployments to cause a kernel crash or limited protocol-state corruption. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53151 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53151 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 REGULAR 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-2026-53151 MODERATE CHECK Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';CWE-125;*CWE-20;CWE-754;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'AF_RXRPC ACK parsing can incorrectly read the SACK table because rxrpc_input_soft_acks assumed that skb_condense made the received skb data linear and directly accessible. A remote peer may trigger the issue with a deliberately fragmented UDP packet that reaches the ACK processing path, causing an out-of-bounds read candidate or incorrect parsing of ACK state. For the CVSS the PR:N is used because no local user account is required when AF_RXRPC traffic from the attacker is accepted by the target. AC:H is used because reliable triggering depends on packet shape and RXRPC call context rather than a simple generic UDP packet. Impact is at least denial of service via kernel crash or protocol state corruption. For the paranoid score, limited confidentiality or integrity impact is kept because the bug class is an invalid read in a network parser, but there is no clear write primitive in the patch context. AF_RXRPC is normally relevant only on systems using AFS or RXRPC based services, so real exposure depends on whether such traffic is reachable from untrusted networks.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended / not auto-close (with actual score 3) YES SKB PACKET INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=2 ## 1. ActionableScore * Conservative score: 2 * Paranoid score: 4 * Final recommended bucket: **Borderline, manual review recommended / not auto-close** ## 2. Signal breakdown Conservative signals: * Remote reachable / network-triggerable: +2. AF_RXRPC ACK parsing can be reached by network traffic if RXRPC or AFS traffic is accepted by the target. * Memory corruption, weak/indirect corruption candidate: +1. The patch fixes unsafe direct access to SACK data in skb->data when the skb may remain non-linear or fragmented. This is best treated as an invalid/OOB read candidate, not a write primitive. * Reliable kernel crash / strong DoS: +1. Incorrect buffer access in kernel packet parsing can plausibly lead to Oops or crash. * Hard or special trigger conditions: -1. The commit says the fragmented UDP packet would probably need to be deliberately pre-generated, and the packet must reach the RXRPC ACK/SACK path. * Rare/difficult-to-reach subsystem: -1. AF_RXRPC is normally relevant to AFS/RXRPC deployments, not a broad default Internet-facing protocol. Paranoid additional signals: * Confidentiality impact plausible: +1. Limited only for triage sensitivity because an invalid read in a network parser may consume unintended kernel buffer bytes, although no disclosure path is demonstrated. * Integrity impact plausible: +1. Incorrectly parsed SACK state may corrupt RXRPC ACK/retransmission state, but no kernel write primitive or privilege escalation path is shown. Not awarded: * No strong memory corruption bonus. The patch does not show OOB write, UAF, double-free, type confusion, refcount takeover, or arbitrary write. * No strong LPE bonus. There is no demonstrated reclaim, callback dispatch, writable stale object, or controlled overwrite. * No common networking core path bonus. RXRPC is a real network protocol path, but not comparable to TCP/IP core, netfilter packet path, or generic UDP receive logic. ## 3. Reachability analysis A remote peer can potentially trigger the issue by sending crafted RXRPC ACK traffic using a deliberately fragmented UDP packet, if AF_RXRPC traffic is accepted by the target. No local account is required in that network-reachable deployment, so PR would be treated as none for network CVSS-style reasoning. Realistic exposure is narrower than generic UDP because RXRPC is mainly used with AFS/RXRPC services and is not commonly exposed on public Internet hosts. Namespaces do not materially lower the trigger requirement for the remote case, but local RXRPC traffic generation could also be possible from an unprivileged local process if the protocol is available. ## 4. Severity interpretation This behaves more like a borderline/actionable Moderate network parser bug than a clear Important vulnerability. The theoretical concern is an invalid/OOB read from non-linear skb data in a remote packet parsing path. The realistic evidence supports crash or protocol-state corruption more strongly than confidentiality disclosure, integrity compromise, or privilege escalation. Because it is network reachable and involves unsafe skb buffer access, it should not be auto-closed without review. ## 5. One-sentence report phrase AF_RXRPC ACK parsing may incorrectly read SACK data from a fragmented or non-linear skb after assuming skb_condense made the buffer linear, allowing a remote RXRPC peer in reachable deployments to cause a kernel crash or limited protocol-state corruption. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: the issue is network reachable in affected RXRPC/AFS deployments and involves an invalid/OOB read candidate in kernel packet parsing, even though the patch does not support a strong memory-corruption or LPE primitive. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: rxrpc: Fix the ACK parser to extract the SACK table for parsing Commit: 566c4c1244de50fbff1f89ff93c9d7b0fc256db4 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=566c4c1244de50fbff1f89ff93c9d7b0fc256db4 Commit description: Fix modification of the received skbuff in rxrpc_input_soft_acks() and a potential incorrect access of the buffer in a fragmented UDP packet (the packet would probably have to be deliberately pre-generated as fragmented) when AF_RXRPC tries to extract the contents of the SACK table by copying out the contents of the SACK table into a buffer before attempting to parse AF_RXRPC assumes that it can just call skb_condense() and then validly access the SACK table from skb->data and that it will be a flat buffer - but skb_condense() can silently fail to do anything under some circumstances. Note that whilst rxrpc_input_soft_acks() should be able to parse extended ACKs, the rest of AF_RXRPC doesn't currently support that. Further, there's then no need to call skb_condense() in rxrpc_input_ack(), so don't. Fixes: d57a3a1 ("rxrpc: Save last ACK's SACK table rather than marking txbufs") Reported-by: Michael Bommarito Link: https://lore.kernel.org/r/20260513180907.2061972-1-michael.bommarito@gmail.com Signed-off-by: David Howells cc: Marc Dionne cc: Jeffrey Altman cc: Eric Dumazet cc: "David S. Miller" cc: Jakub Kicinski cc: Paolo Abeni cc: Simon Horman cc: linux-afs@lists.infradead.org cc: netdev@vger.kernel.org cc: stable@kernel.org Link: https://patch.msgid.link/105362.1780573560@warthog.procyon.org.uk Signed-off-by: Paolo Abeni Signed-off-by: Greg Kroah-Hartman Changed files: net/rxrpc/input.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=566c4c1244de50fbff1f89ff93c9d7b0fc256db4 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53151 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53151 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: AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS score: 7 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: 2 Paranoid ActionableScore: 4 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: NO Published priority for this report (same as in Subject): MODERATE REGULAR 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).