From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-99136][MODERATE REGULAR] dm-crypt: fix a tiny race condition in crypt_dec_pending Date: Thu, 29 Oct 2026 00:41:32 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-99136 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: 3 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: ac5d887ab93592fc5e3605fe30c1d8d232d609b3 List-Id: CVE: CVE-2026-99136 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: dm-crypt: fix a tiny race condition in crypt_dec_pending Commit: ac5d887ab93592fc5e3605fe30c1d8d232d609b3 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ac5d887ab93592fc5e3605fe30c1d8d232d609b3 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99136 Analysis date: Thu, 29 Oct 2026 00:41:32 -0400 ActionableScore: 3 ActionableScore lower bound: unknown Actionable bucket: Borderline / manual review recommended Manual review required: YES Summary: A narrow dm-crypt completion race can report failed, potentially undecrypted or unwritten I/O as successful, causing silent storage-integrity failure without a shown memory-corruption or privilege-escalation primitive. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99136 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99136 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-2026-99136 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-99136 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE RESULT=DIFF (final Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H';CWE-362;CWE-662;CWE-703;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:L';BEST CVSS score: '6.3';DESCR 'A race in crypt_dec_pending can read io error before another completion context records an I O failure and releases its reference. If the stale success status is used when the final reference is dropped, a failed read that was not decrypted or a failed write can be reported as successful, creating silent storage integrity loss and possible availability damage. For the CVSS the PR:L value reflects that practical triggering requires a local user or process able to issue I O through the affected dm crypt mapping. Reliable exploitation also depends on inducing a backing I O failure inside the narrow race window, so AC:H is appropriate. The issue is not directly network reachable. There is no UAF, OOB access, information leak, or arbitrary write primitive supported by the code change, so confidentiality impact and privilege escalation are not assigned. Automated impact decision path. The original SimpleNet classifier selected IMPORTANT. The primary LLM estimated paranoid CVSS 6.3 and the production ActionableScore returned 3 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage IMPORTANT to MODERATE_KPANIC because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE_KPANIC to MODERATE because the ActionableScore threshold rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS and DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and V41_INHERITED_KPANIC_PROMOTION_BLOCKED and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 2.5 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3) MAYBE DISK RACE LEAK UAF LINUS LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 V41_INHERITED_KPANIC_PROMOTION_BLOCKED MANUAL_REVIEW_REQUIRED - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=3 PrimitiveClass=CLASS_B RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES RequiresHostUID0=NO AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw base score: 3 * Conservative score: 3 * Raw paranoid score: 3 * Paranoid score: 3 * No floor or cap applied. * Final recommended bucket: **Borderline / manual review recommended**:: 2. Signal breakdown * +1 Local below-host-admin trigger: supplied evidence grounds a local process issuing I/O through an accessible dm-crypt mapping. * +1 Integrity plausible: a failed read or write can be completed with a stale success status, hiding an actual storage failure. * +1 Important storage path: dm-crypt completion status directly governs encrypted block-I/O error reporting. * +1 Broad exposure: dm-crypt is widely deployed and `crypt_dec_pending()` is on its normal completion path. * -1 Hard timing requirement: exploitation requires a backing-I/O failure and a narrow ordering between `io->error` update/reference drop and the stale read. Not awarded: no UAF, OOB access, arbitrary write, kernel crash, disclosure, authorization bypass, protected-victim overwrite, or privilege escalation is shown. Availability damage is possible but not sufficiently concrete for a separate point. 3. Reachability analysis A local process with permission to issue I/O through an existing dm-crypt-backed resource can reach the completion path without host-administrator powers. Creation of the mapping normally involves prior privileged system configuration, but the later I/O issuer need not create it. Trigger reliability additionally depends on inducing or encountering a backing-device I/O failure during the narrow race window. No namespace capability or special hardware requirement is shown. 4. Primitive and severity reading The primitive is a stale completion-status race: `io->error` was sampled before the final ordered reference decrement, while another completion context could record an error before the bio was completed. This is semantic active-state consumption, not memory corruption or lifetime misuse, and is classified CLASS_B because it can silently misreport failed storage operations. The shown impact is integrity loss in I/O completion semantics. Actual corruption of another principal’s protected data, persistent disk corruption, host crash, or LPE remains unproven. The issue therefore does not meet NEW52/B5-R, B3-PENDING, or B4-PENDING. ImportantCandidate is NO, and auto-downgrade remains allowed, although human review is advisable because silent successful completion can conceal real storage failures. 5. One-sentence report phrase A narrow dm-crypt completion race can report failed, potentially undecrypted or unwritten I/O as successful, causing silent storage-integrity failure without a shown memory-corruption or privilege-escalation primitive. 6. Manual review advice MANUAL CHECK RECOMMENDED Confirm whether realistic workloads let a below-host-admin I/O issuer induce repeatable backing failures and whether stale success can affect shared or security-sensitive storage consumers. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: dm-crypt: fix a tiny race condition in crypt_dec_pending Commit: ac5d887ab93592fc5e3605fe30c1d8d232d609b3 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ac5d887ab93592fc5e3605fe30c1d8d232d609b3 Commit description: crypt_dec_pending reads io->error before calling atomic_dec_and_test. Another context, for example crypt_endio called from an interrupt, may set io->error and drop its reference between the read and the decrement. crypt_dec_pending then drops the last reference and completes the bio with the stale status - so a read that failed and was never decrypted, or a write that failed, is reported as successful. The read was placed before the decrement by commit b35f8ca ("dm crypt: wait for endio to complete before destruction"), because that commit freed dm_crypt_io before calling bio_endio. This is no longer the case, dm_crypt_io lives in the per-bio data now. Read io->error after atomic_dec_and_test instead. atomic_dec_and_test is fully ordered, so no additional barrier is needed. Fixes: b35f8ca ("dm crypt: wait for endio to complete before destruction") Cc: stable@vger.kernel.org Reviewed-by: Jose Fernandez (Anthropic) Signed-off-by: Ben Cressey Assisted-by: Claude:unspecified Signed-off-by: Mikulas Patocka Signed-off-by: Greg Kroah-Hartman Changed files: drivers/md/dm-crypt.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=ac5d887ab93592fc5e3605fe30c1d8d232d609b3 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99136 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99136 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:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:L The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H The Best / paranoid CVSS score: 6.3 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: 3 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).