From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-53311][LOW] fuse: fix uninit-value in fuse_dentry_revalidate() Date: Fri, 26 Jun 2026 16:05:58 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-53311 X-AL-KERNEL-Priority: LOW X-AL-KERNEL-Severity: LOW X-AL-KERNEL-Base-Severity: LOW X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 2 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: da3d241c5b925f17a9d8051d7a9e0d454d8e01f6 List-Id: CVE: CVE-2026-53311 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: fuse: fix uninit-value in fuse_dentry_revalidate() Commit: da3d241c5b925f17a9d8051d7a9e0d454d8e01f6 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=da3d241c5b925f17a9d8051d7a9e0d454d8e01f6 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53311 Analysis date: Fri, 26 Jun 2026 16:05:58 -0400 ActionableScore: 2 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate / Low-like Manual review required: NO Summary: FUSE dentry revalidation could read an uninitialized dentry d_time value during local pathname lookup, causing cache validation decisions to depend on stale allocator contents with limited integrity impact and no demonstrated memory corruption primitive. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53311 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53311 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: LOW 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-2026-53311 LOW CHECK Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L';*CWE-457;CWE-665;CWE-754;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N';BEST CVSS score: '4.4';DESCR 'FUSE dentry revalidation can read an uninitialized dentry d_time value when a newly allocated dentry reaches fuse_dentry_revalidate through the lookup_open path. The value is used in cache invalidation logic against the FUSE epoch, so an uninitialized value can make the dentry validation decision depend on stale allocator contents rather than a defined initial state. For the CVSS the PR:L is used because a local user or process must access a FUSE mount or otherwise trigger local pathname lookup activity. The issue is not network reachable. Impact is mainly a limited integrity concern from incorrect dentry cache validation, with possible limited availability impact in debug or sanitizer builds. There is no clear UAF, OOB access, arbitrary write, or direct information leak primitive supported by the patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) SKIP CVE-2026-53311 SKIP The Fixes patch not applied yet, so unlikely that actual: 2396356a945bb022aff02656f59c2a45d457043f YES NO NO unknown MAYBE READ KASAN DISK INIT NOMEMCHK LINUS SYZBOT - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 ## 1. ActionableScore * Conservative score: 2 * Paranoid score: 2 * Final recommended bucket: **Ordinary Moderate / Low-like**:: ## 2. Signal breakdown * Local unprivileged trigger: +1 A local user or process can plausibly trigger pathname lookup activity on a FUSE mount. * Integrity impact plausible: +1 The uninitialized `dentry->d_time` value can affect FUSE dentry cache revalidation decisions, potentially causing incorrect cache validity behavior. * No generic memory corruption: +0 The patch shows initialization of a scalar dentry timestamp field, not UAF, OOB write, double-free, type confusion, or arbitrary write. * No reliable kernel crash / strong DoS: +0 The issue was detected by KMSAN as an uninitialized value read. The patch does not indicate a production kernel panic path. * No confidentiality primitive: +0 There is no user-visible leak of the uninitialized value. * No Important filesystem metadata corruption signal: +0 This affects FUSE dentry validation state, not persistent filesystem metadata or page-cache ownership. ## 3. Reachability analysis A local process needs access to a FUSE mount and must trigger lookup/open paths that create and revalidate a newly allocated dentry. This is not network reachable. User namespaces may make FUSE usage more common in containerized or desktop-like environments, but the bug still requires local filesystem activity rather than remote input. FUSE is common, but this specific issue is a local cache-validation logic bug with no demonstrated corruption primitive. ## 4. Severity interpretation This behaves like an ordinary Moderate or Low-like issue rather than an Important-class kernel vulnerability. The theoretical impact is incorrect FUSE dentry cache validation caused by use of an uninitialized scalar field. Realistic exploitation evidence supports limited integrity impact at most, not privilege escalation, memory corruption, or sensitive data disclosure. ## 5. One-sentence report phrase FUSE dentry revalidation could read an uninitialized dentry d_time value during local pathname lookup, causing cache validation decisions to depend on stale allocator contents with limited integrity impact and no demonstrated memory corruption primitive. ## 6. Manual review recommendation NO MANUAL CHECK NEEDED This can be auto-closed for urgent triage purposes because the ActionableScore is below 3, the best CVSS hint is 4.4, and the patch context supports only a local uninitialized scalar logic bug without UAF, OOB access, arbitrary write, info leak, or realistic LPE path. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: fuse: fix uninit-value in fuse_dentry_revalidate() Commit: da3d241c5b925f17a9d8051d7a9e0d454d8e01f6 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=da3d241c5b925f17a9d8051d7a9e0d454d8e01f6 Commit description: fuse_dentry_revalidate() may be called with a dentry that didn't had ->d_time initialised. The issue was found with KMSAN, where lookup_open() calls __d_alloc(), followed by d_revalidate(), as shown below: ===================================================== BUG: KMSAN: uninit-value in fuse_dentry_revalidate+0x150/0x13d0 fs/fuse/dir.c:394 fuse_dentry_revalidate+0x150/0x13d0 fs/fuse/dir.c:394 d_revalidate fs/namei.c:1030 [inline] lookup_open fs/namei.c:4405 [inline] open_last_lookups fs/namei.c:4583 [inline] path_openat+0x1614/0x64c0 fs/namei.c:4827 do_file_open+0x2aa/0x680 fs/namei.c:4859 [...] Uninit was created at: slab_post_alloc_hook mm/slub.c:4466 [inline] slab_alloc_node mm/slub.c:4788 [inline] kmem_cache_alloc_lru_noprof+0x382/0x1280 mm/slub.c:4807 __d_alloc+0x55/0xa00 fs/dcache.c:1740 d_alloc_parallel+0x99/0x2740 fs/dcache.c:2604 lookup_open fs/namei.c:4398 [inline] open_last_lookups fs/namei.c:4583 [inline] path_openat+0x135f/0x64c0 fs/namei.c:4827 do_file_open+0x2aa/0x680 fs/namei.c:4859 [...] ===================================================== Reported-by: syzbot+fdebb2dc960aa56c600a@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/69917e0d.050a0220.340abe.02e2.GAE@google.com Fixes: 2396356 ("fuse: add more control over cache invalidation behaviour") Signed-off-by: Luis Henriques Signed-off-by: Miklos Szeredi Signed-off-by: Sasha Levin Changed files: fs/fuse/dir.c fs/namei.c mm/slub.c fs/dcache.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=da3d241c5b925f17a9d8051d7a9e0d454d8e01f6 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53311 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53311 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:L/PR:L/UI:N/S:U/C:N/I:L/A:N The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L The Best / paranoid CVSS score: 4.4 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: 2 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: LOW KPANIC detected for this report: NO Published priority for this report (same as in Subject): LOW 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).