From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-53272][MODERATE 7.0] erofs: fix use-after-free on sbi->sync_decompress [ Upstream Date: Thu, 25 Jun 2026 10:29:56 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-53272 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 5 X-AL-KERNEL-ActionableScore-Lower: 3 X-AL-KERNEL-Commit: 86ab00cf81d44b675bb23db62b88fd76c8ac8cea List-Id: CVE: CVE-2026-53272 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: erofs: fix use-after-free on sbi->sync_decompress [ Upstream Commit: 86ab00cf81d44b675bb23db62b88fd76c8ac8cea Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=86ab00cf81d44b675bb23db62b88fd76c8ac8cea Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53272 Analysis date: Thu, 25 Jun 2026 10:29:56 -0400 ActionableScore: 5 ActionableScore lower bound: 3 Actionable bucket: Actionable Moderate at minimum Manual review required: YES Summary: A race between EROFS compressed I/O completion and filesystem unmount can leave `z_erofs_decompress_kickoff()` accessing `sbi->sync_decompress` after the superblock private data is freed, causing a local UAF with reliable DoS and limited but defensible privilege-escalation concern. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53272 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53272 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-2026-53272 MODERATE CHECK Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in the EROFS compressed data path can allow z_erofs_decompress_kickoff() to access sbi sync_decompress after the filesystem superblock private data has been freed during unmount. The vulnerable sequence is I/O completion, asynchronous decompression work queueing, folio unlock, unmount cleanup, and then a later access to the freed sbi field. This is a use-after-free condition rather than a pure crash-only logic bug because the old code can read and update a field in freed memory. A realistic base interpretation may require administrative mount or unmount control, but For the CVSS the PR:L is used for the paranoid score because local users in delegated mount namespaces, container root, or service contexts may be able to influence EROFS I/O and teardown timing without full host root privileges. The issue is not network reachable. Impact is at least local denial of service via kernel crash and in the worst case may allow confidentiality and integrity impact due to memory corruption, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4) YES DANGER DISK RACE UAF HARDWARE LINUS SYZBOT DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=3 ## 1. ActionableScore * Conservative score: 3 * Paranoid score: 5 * Final recommended bucket: **Actionable Moderate at minimum** ## 2. Signal breakdown * Generic memory corruption: +2. The patch fixes a real use-after-free on `sbi->sync_decompress`. * Real lifetime corruption: +1. The bug is an async completion versus unmount lifetime mismatch where `sbi` can be freed before later access. * Reliable kernel crash / strong DoS: +1. A UAF in filesystem decompression teardown can realistically crash the kernel, especially under KASAN or unlucky reuse. * Important filesystem/storage path: +1. The bug is in EROFS compressed I/O/decompression handling during filesystem teardown. * Hard or unreliable race: -1. Triggering requires a timing window between I/O completion, queued decompression work, folio unlock, and unmount. * Privilege requirement: -1 conservative. Typical triggering requires mount/unmount control, but delegated mount namespaces, container root, or service-managed mounts may reduce practical privilege assumptions. * Constrained corruption: -1 paranoid. The stale access is to a specific `sync_decompress` field and the write value is a fixed enum, not an attacker-chosen arbitrary write. * Weak LPE concern: +1 paranoid. Because this is a writable UAF on freed filesystem private data, limited privilege-escalation concern is defensible even though no reclaim or object-replacement primitive is shown. CWE: CWE-416, CWE-362, CWE-667. ## 3. Reachability analysis The bug is locally reachable through EROFS compressed filesystem activity combined with unmount timing. In typical host deployments, mounting and unmounting EROFS images requires administrative privileges or `CAP_SYS_ADMIN`, so the conservative score is lower. In container, namespace, appliance, Android, or service-managed image environments, a less privileged actor may be able to influence EROFS I/O and teardown indirectly, so the paranoid score treats the issue as actionable. This is not network reachable. The affected path is not a universal default path, but EROFS is a real deployed filesystem and the bug is in a normal compressed read/decompression lifetime path. ## 4. Severity interpretation This is more than an ordinary Moderate crash because the patch fixes a real UAF with a stale read and possible stale write after `sbi` is freed. Realistic exploitation evidence supports local DoS more strongly than privilege escalation. Theoretical LPE is plausible enough for manual review because freed filesystem private memory may be reused, but the patch does not show attacker-controlled reclaim, callback corruption, type confusion, refcount takeover, or arbitrary write. Overall this is an Actionable Moderate at minimum, not an auto-close candidate. ## 5. One-sentence report phrase A race between EROFS compressed I/O completion and filesystem unmount can leave `z_erofs_decompress_kickoff()` accessing `sbi->sync_decompress` after the superblock private data is freed, causing a local UAF with reliable DoS and limited but defensible privilege-escalation concern. ## 6. Manual review recommendation MANUAL CHECK REQUIRED. Reason: this is a real race-based UAF with a writable stale access in a filesystem decompression path. The practical impact is likely local DoS, but the memory lifetime primitive is strong enough to require manual review for possible allocator reuse and privilege-escalation feasibility. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: erofs: fix use-after-free on sbi->sync_decompress [ Upstream Commit: 86ab00cf81d44b675bb23db62b88fd76c8ac8cea Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=86ab00cf81d44b675bb23db62b88fd76c8ac8cea Changed files: fs/erofs/zdata.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=86ab00cf81d44b675bb23db62b88fd76c8ac8cea ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53272 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53272 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:H/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/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: 3 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: NO 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).