From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-45999][MODERATE REGULAR] erofs: fix unsigned underflow in z_erofs_lz4_handle_overlap() [ Upstream Date: Wed, 27 May 2026 11:29:03 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-45999 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: 1 X-AL-KERNEL-Commit: 43a878639b90e9721ffa5eb616a7e6d8454adef3 List-Id: CVE: CVE-2026-45999 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: erofs: fix unsigned underflow in z_erofs_lz4_handle_overlap() [ Upstream Commit: 43a878639b90e9721ffa5eb616a7e6d8454adef3 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=43a878639b90e9721ffa5eb616a7e6d8454adef3 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45999 Analysis date: Wed, 27 May 2026 11:29:03 -0400 ActionableScore: 3 ActionableScore lower bound: 1 Actionable bucket: Borderline, manual review recommended Manual review required: YES Summary: A crafted EROFS image can trigger unsigned underflow in the LZ4 inplace overlap path, causing an OOB read past the decompressed pages array and likely local DoS during filesystem parsing. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-45999 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45999 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-2026-45999 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:L/I:L/A:H';CWE-191;CWE-125;*CWE-20;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A crafted EROFS image can make the LZ4 inplace overlap path run with outpages lower than inpages. This makes rq outpages minus rq inpages underflow and can read past the rq out decompressed_pages array during z_erofs_lz4_handle_overlap(). For the CVSS the PR:L is used in the paranoid score because some systems may let less trusted users provide filesystem images through automount, container image, Android, embedded update, appliance, or scanner workflows. The typical host case is closer to PR:H because mounting a crafted filesystem image usually requires administrative privileges. The issue is not network reachable by itself and does not involve UAF, out of bounds write, arbitrary write, or privilege escalation. Impact is primarily denial of service via kernel crash or filesystem corruption handling, with only limited confidentiality or integrity concern from kernel parser out of bounds read behavior.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 2) YES OOB DANGER DISK IMPROVEONLY LINUS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=3 ActionableScoreLower=1 ## 1. ActionableScore * Conservative score: 1 * Paranoid score: 3 * Final recommended bucket: **Borderline, manual review recommended**:: ## 2. Signal breakdown Conservative signals: * Important filesystem/storage path: +1 The bug is in EROFS decompression and filesystem image parsing. * Reliable crash / DoS plausible: +1 The crafted image can drive an out-of-bounds read past `decompressed_pages`, likely causing a crash, corruption report, or fault. * Availability impact realistic: +1 Mounting and reading the crafted image can disrupt the kernel path handling that filesystem. Subtracting signals: * Requires admin/CAP_SYS_ADMIN in typical deployments: -2 Mounting a crafted EROFS image normally requires administrative privileges. * Constrained read-only primitive: -1 The supported primitive is OOB read due to unsigned underflow, not OOB write, UAF, arbitrary write, or object lifetime corruption. Paranoid additions: * Local delegated image-processing concern: +1 Some environments process EROFS images from less trusted users through automount, container images, Android or embedded update flows, appliance pipelines, or scanners. * Weak confidentiality/integrity concern: +1 Kernel filesystem parser OOB reads can occasionally expose or misinterpret adjacent metadata, but no direct disclosure or write primitive is shown. ## 3. Reachability analysis The bug is triggered by a crafted EROFS image with illegal compressed extents that force the LZ4 inplace overlap path with `outpages < inpages`. In normal host deployments, the attacker needs the ability to mount or otherwise make the kernel parse the crafted image. Namespaces and containers can reduce effective privilege if image mounting or scanning is delegated. It is not network reachable by itself. Practical exposure is higher in Android, embedded, container-image, appliance-update, or automated filesystem scanning workflows. ## 4. Severity interpretation This is a borderline Moderate filesystem parser issue. It is not an Important memory-corruption issue based on the patch alone because the visible primitive is an OOB read, not a write, UAF, refcount bug, or page-cache corruption. Realistic impact is DoS or filesystem corruption handling after parsing a crafted image. Theoretical C/I impact is limited and should be manually checked only in environments that ingest untrusted EROFS images. ## 5. One-sentence report phrase A crafted EROFS image can trigger unsigned underflow in the LZ4 inplace overlap path, causing an OOB read past the decompressed pages array and likely local DoS during filesystem parsing. ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED Reason: this is an OOB read in kernel filesystem decompression code and may be relevant where untrusted EROFS images are mounted or processed, but no OOB write, UAF, or privilege-escalation primitive is shown. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: erofs: fix unsigned underflow in z_erofs_lz4_handle_overlap() [ Upstream Commit: 43a878639b90e9721ffa5eb616a7e6d8454adef3 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=43a878639b90e9721ffa5eb616a7e6d8454adef3 Changed files: fs/erofs/decompressor.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=43a878639b90e9721ffa5eb616a7e6d8454adef3 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-45999 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45999 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:N/I:N/A:H The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS score: 5.8 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: 1 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).