From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-89606][MODERATE 7.0] ecryptfs: reject too-small tag 70 packets Date: Fri, 11 Sep 2026 20:37:42 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-89606 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: 9d88391bbed76eb091cddd50b0af87b1c6f22589 List-Id: CVE: CVE-2026-89606 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: ecryptfs: reject too-small tag 70 packets Commit: 9d88391bbed76eb091cddd50b0af87b1c6f22589 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9d88391bbed76eb091cddd50b0af87b1c6f22589 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89606 Analysis date: Fri, 11 Sep 2026 20:37:42 -0400 ActionableScore: 5 ActionableScore lower bound: 4 Actionable bucket: Actionable Moderate Manual review required: NO Summary: A malformed eCryptfs tag 70 filename packet can underflow the encrypted filename size calculation in ecryptfs_parse_tag_70_packet, causing invalid parser behavior and possible local denial of service, with manual review needed for downstream length handling impact. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-89606 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89606 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-2026-89606 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89606 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';CWE-191;*CWE-20;CWE-125;**CWE-400;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H';BEST CVSS score: '6.6';DESCR 'An integer underflow in ecryptfs_parse_tag_70_packet can occur when a malformed tag 70 filename encryption packet is smaller than the fixed metadata fields. The underflow can produce a very large encrypted filename size and may lead to invalid memory reads, excessive allocation attempts, or a kernel crash when the malformed filename is parsed. For the CVSS the PR:L is used because practical triggering requires a local user or process able to supply or access crafted eCryptfs backing filenames. The issue is not network reachable by itself and depends on local filesystem exposure of eCryptfs encrypted names. Impact is at least local denial of service via parser failure or kernel crash and in worst case may allow limited confidentiality or integrity impact due to the underflowed length handling. YES REQUIRES MANUAL CHECK.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate (with actual score 5) SKIP CVE-2026-89606 UNKNOWN SKIP No affected files built, so skip this CVE NO - - unknown MAYBE OOB DISK SIMPLEFIX LINUS KPANIC PACKET - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=4 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=NO ## 1. ActionableScore * Raw conservative score: 4 * Conservative score: 4 * Raw paranoid score: 5 * Paranoid score: 5 * Final recommended bucket: **Actionable Moderate**:: No floor or cap changed the conservative score. No floor or cap changed the paranoid score. ## 2. Signal breakdown Conservative signals: * +1 Weak / indirect corruption candidate: the malformed tag 70 packet can underflow a `size_t` filename size calculation and produce a bogus large length. * +1 Memory layout invariant restoration: the fix restores the required minimum packet layout before subtracting fixed metadata fields. * +1 Local attacker-controlled parser input: a local user or process with access to crafted eCryptfs backing filenames can plausibly trigger parsing of malformed encrypted filename metadata. * +1 Reliable DoS / strong availability concern: the underflowed length may lead to invalid reads, excessive allocation attempts, parser failure, or kernel crash. Paranoid additional signal: * +1 Unresolved kernel parser impact: the underflowed length is used in filename parsing/decryption logic, and full downstream consequences are not visible from this small patch. This supports manual review sensitivity but does not prove arbitrary write or LPE. Non-awarded signals: * Controlled reclaim not demonstrated. * Arbitrary write not demonstrated. * Real UAF not demonstrated. * Concrete repeated release/refcount mutation not present. * Confidentiality impact not awarded because no user-visible kernel disclosure path is established. * Integrity impact not awarded because no unauthorized write or protected-object modification is established. * Remote reachability not established. * Extra Availability not awarded beyond the same crash/resource failure path. * ImportantCandidate not set because the patch supports an integer-underflow parser bug, not a strong memory-corruption or security-boundary primitive. ## 3. Reachability analysis The trigger is local filesystem/parser reachability. A crafted eCryptfs tag 70 filename packet must be supplied or encountered so that `ecryptfs_parse_tag_70_packet()` parses it. Host-admin-equivalent privilege is not positively required by the supplied context. The practical attacker model is a local user or local process able to place or access malformed eCryptfs encrypted filenames in a relevant backing directory or filesystem image. This is below host-admin in plausible deployments, so `HostAdminRequired=NO`. No direct network path is shown. Namespace-scoped privilege is not central to this issue and the supplied evidence does not establish a namespace-specific complete trigger chain, so `NamespaceScopedPrivilege=UNKNOWN`. No race is involved. No special hardware is involved. Prior setup may include an eCryptfs mount or an existing eCryptfs-backed directory, but the vulnerable operation itself is parser-side handling of malformed filename metadata. ## 4. Primitive and severity interpretation The exact primitive is an integer underflow in `ecryptfs_parse_tag_70_packet()` when `parsed_tag_70_packet_size` is smaller than the fixed tag 70 metadata fields. The resulting `block_aligned_filename_size` may become a very large `size_t` value. This is not a UAF and not a repeated lifetime/refcount mutation. It is also not a demonstrated arbitrary read/write primitive. The established class is malformed input leading to invalid size computation in a kernel filesystem parser, with likely consequences in the DoS / invalid-read / excessive-allocation range. PrimitiveClass is `CLASS_C` because the demonstrated behavior is primarily invalid-state and DoS-oriented, without an independently useful corruption primitive. The paranoid score keeps the issue actionable because integer underflow in filesystem parser length handling can have non-obvious downstream effects and should not be automatically closed from the small patch alone. ImportantCandidate is `NO` because no strong exploitation leverage, ownership/COW bypass, authorization bypass, UAF, arbitrary write, or LPE path is established. AutoDowngradeAllowed is `NO` because the underflowed length is a concrete kernel parser primitive with unresolved downstream effects and should receive manual review before closure. Likely operational severity: Actionable Moderate. ## 5. One-sentence report phrase A malformed eCryptfs tag 70 filename packet can underflow the encrypted filename size calculation in ecryptfs_parse_tag_70_packet, causing invalid parser behavior and possible local denial of service, with manual review needed for downstream length handling impact. ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED Reason: the patch fixes a concrete integer underflow in kernel filesystem parser length handling, and the downstream impact of the underflowed filename size is not fully visible from the supplied diff. ## 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: ecryptfs: reject too-small tag 70 packets Commit: 9d88391bbed76eb091cddd50b0af87b1c6f22589 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9d88391bbed76eb091cddd50b0af87b1c6f22589 Commit description: ecryptfs_parse_tag_70_packet() subtracts fixed metadata fields from the parsed packet body size to derive the encrypted filename size. A malformed packet with a body smaller than those fixed fields can underflow that size calculation. Reject tag 70 packets before the subtraction unless the body contains the signature, cipher code, and at least one byte of encrypted filename data. Fixes: 9c79f34 ("eCryptfs: Filename Encryption: Tag 70 packets") Cc: Signed-off-by: Yichong Chen Signed-off-by: Tyler Hicks Signed-off-by: Greg Kroah-Hartman Changed files: fs/ecryptfs/keystore.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=9d88391bbed76eb091cddd50b0af87b1c6f22589 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-89606 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89606 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:L/I:N/A:H The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS score: 6.6 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).