From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74433][MODERATE 7.0] rxrpc: Fix UAF in rxgk_issue_challenge() Date: Sun, 16 Aug 2026 02:20:29 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74433 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: 4 X-AL-KERNEL-Commit: 844b8525ce503405c462ad67f750bec648720397 List-Id: CVE: CVE-2026-74433 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: rxrpc: Fix UAF in rxgk_issue_challenge() Commit: 844b8525ce503405c462ad67f750bec648720397 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=844b8525ce503405c462ad67f750bec648720397 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74433 Analysis date: Sun, 16 Aug 2026 02:20:29 -0400 ActionableScore: 5 ActionableScore lower bound: 4 Actionable bucket: Actionable Moderate at minimum Manual review required: NO Summary: A use-after-free in `rxgk_issue_challenge()` can occur because the challenge page is freed before `trace_rxrpc_tx_packet()` uses `whdr` pointing into that page, making this a network-adjacent RxRPC lifetime bug with realistic DoS impact and limited but manual-review-worthy corruption concern. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74433 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74433 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: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-74433 MODERATE CHECK WITH IMPACT FROM ORIG NN MODERATE 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-416;CWE-825;*CWE-672;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '7';DESCR 'A use-after-free can occur in rxgk_issue_challenge() because the page holding the challenge packet is freed before trace_rxrpc_tx_packet() uses whdr that points into that page. The visible primitive is a stale pointer read in the tracepoint path rather than an obvious write primitive, so the realistic impact is limited denial of service or diagnostic UAF when tracing or debug checks are active. For the CVSS the PR:N is used for the paranoid network case because a remote peer may trigger challenge generation without local user access when the RxRPC rxgk service and tracing path are reachable. The issue is network reachable in affected RxRPC deployments, but practical triggering depends on non-default rxgk usage and tracepoint or debug visibility. Impact is at least availability loss and in the paranoid case may include limited confidentiality or integrity impact due to the use-after-free class, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5) SKIP CVE-2026-74433 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 9d1d2b59341f58126a69b51f9f5f8ccb9f12e54a YES NO NO unknown MAYBE INIT UAF LINUS KPANIC - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=4 ## 1. ActionableScore * Conservative score: 4 * Paranoid score: 5 * Final recommended bucket: **Actionable Moderate at minimum** ## 2. Signal breakdown Conservative signals: * Remote reachable / network-triggerable: +2 `rxgk_issue_challenge()` is in RxRPC challenge generation and can plausibly be reached due to remote peer activity when RxRPC rxgk is in use. * Memory corruption, weak/indirect corruption candidate: +1 The patch fixes a real UAF, but the visible primitive is a stale pointer passed to a tracepoint and apparently read for tracing. No write-after-free, reclaim control, callback control, or type confusion is shown. * Real lifetime corruption: +1 `whdr` points into a page that was freed before `trace_rxrpc_tx_packet()` used it. * Reliable kernel crash / strong DoS: +1 A UAF read in tracing/debug paths can plausibly trigger KASAN reports, warnings, or kernel crashes when the tracepoint/debug configuration is active. * Rare AND difficult-to-reach subsystem/configuration: -1 The affected path depends on RxRPC rxgk/GSSAPI usage and the problematic dereference appears tied to tracepoint consumption, which is not a broad default packet path. Paranoid adjustment: * Paranoid score removes the rare/configuration penalty for environments where RxRPC rxgk and tracing are intentionally enabled and reachable. This raises the practical triage score from 4 to 5. Not awarded: * Strong LPE plausibility: +0 The patch does not show attacker-controlled reclaim, object replacement, write-after-free, type confusion, callback dispatch, or refcount takeover. * Confidentiality / Integrity impact: +0 in the conservative score The demonstrated primitive is stale read/use by a tracepoint, not a user-visible info leak or attacker-controlled write. ## 3. Reachability analysis A remote RxRPC peer may be able to cause challenge generation if the target uses the rxgk security class. However, rxgk/GSSAPI RxRPC is not a common default Internet-facing configuration. The UAF is most relevant when the tracepoint path actually consumes `whdr`; if tracing is disabled, practical impact may be much lower. No local privileges are required in the network-triggered interpretation, but realistic triggering requires a reachable affected RxRPC deployment. Namespaces and containers do not materially improve reachability unless they expose or route access to the relevant RxRPC service. Call-site confidence: medium. The vulnerable function and immediate use-after-free ordering are visible, but broader deployment and tracepoint activation details are not fully shown in the supplied patch. ## 4. Severity interpretation This is not an ordinary low-priority cleanup because it is a real UAF in network-adjacent kernel code. At the same time, the shown primitive is weak: a stale pointer is used by a tracepoint after the backing page is freed, with no demonstrated attacker-controlled reuse or write primitive. Realistically, this behaves like an actionable Moderate issue: network-reachable in affected deployments, memory-lifetime bug class, likely DoS/debug UAF impact. It is not a strong Important candidate unless additional evidence shows attacker-controlled reclaim, disclosure through trace buffers available to lower-privileged users, or a stronger corruption path. ## 5. One-sentence report phrase A use-after-free in `rxgk_issue_challenge()` can occur because the challenge page is freed before `trace_rxrpc_tx_packet()` uses `whdr` pointing into that page, making this a network-adjacent RxRPC lifetime bug with realistic DoS impact and limited but manual-review-worthy corruption concern. ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED Reason: this is a real UAF in a network-adjacent RxRPC path, but the visible primitive is limited to tracepoint use after free and does not currently demonstrate LPE, arbitrary write, or attacker-controlled object reuse. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: rxrpc: Fix UAF in rxgk_issue_challenge() Commit: 844b8525ce503405c462ad67f750bec648720397 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=844b8525ce503405c462ad67f750bec648720397 Commit description: Fix rxgk_issue_challenge() to free the page containing the challenge content after invoking the tracepoint as the whdr passed to the tracepoint points into the page just freed. Fixes: 9d1d2b5 ("rxrpc: rxgk: Implement the yfs-rxgk security class (GSSAPI)") Reported-by: Marc Dionne Signed-off-by: David Howells cc: Simon Horman cc: linux-afs@lists.infradead.org cc: stable@kernel.org Link: https://patch.msgid.link/20260609140911.838677-4-dhowells@redhat.com Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman Changed files: net/rxrpc/rxgk.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=844b8525ce503405c462ad67f750bec648720397 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74433 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74433 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:L 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: 4 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).