From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-80843][LOW] xfrm: fix xfrm_state_construct() auth-trunc leak Date: Fri, 04 Sep 2026 15:50:21 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-80843 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: 1 X-AL-KERNEL-Commit: 958ae9f261319e1cdc44879886bcda2263258cca List-Id: CVE: CVE-2026-80843 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: xfrm: fix xfrm_state_construct() auth-trunc leak Commit: 958ae9f261319e1cdc44879886bcda2263258cca Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=958ae9f261319e1cdc44879886bcda2263258cca Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80843 Analysis date: Fri, 04 Sep 2026 15:50:21 -0400 ActionableScore: 2 ActionableScore lower bound: 1 Actionable bucket: Ordinary Moderate Manual review required: NO Summary: An XFRM auth-trunc allocation can be leaked during local XFRM state construction when `x.aalg` is overwritten after `props.aalgo` remains zero, allowing possible denial of service through repeated kernel memory leaks but not indicating memory corruption or privilege escalation. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80843 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80843 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-2026-80843 LOW https://www.kernelcve.org/list/?q=CVE-2026-80843 CHECK WITH IMPACT FROM ORIG NN LOW 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:N/A:H';*CWE-401;*CWE-772;**CWE-400;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'The XFRM state construction path can leak an auth algorithm allocation when attach_auth_trunc allocates x.aalg but leaves props.aalgo as zero for an algorithm without a sadb_alg_id such as cmac(aes). The following auth check then treats the state as if no auth algorithm was attached and can overwrite the first allocation, so later error handling or teardown frees only the replacement pointer. For the CVSS the PR:L is used for the paranoid score because delegated CAP_NET_ADMIN or containerized network administration can allow non root service accounts to manage XFRM state in some deployments. The issue is not directly network reachable and is triggered through local XFRM netlink control plane operations. Impact is denial of service via possible kernel memory exhaustion after repeated operations, with no supported evidence of memory corruption, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) SKIP CVE-2026-80843 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE SIMPLEFIX LEAK LINUS INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 ActionableScoreLower=1 PrimitiveClass=NONE RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES ## 1. ActionableScore * Raw conservative score: 1 * Conservative score: 1 * Raw paranoid score: 2 * Paranoid score: 2 * Final recommended bucket: **Ordinary Moderate**:: No floor or cap was applied. ## 2. Signal breakdown Conservative signals: * +1 Concrete persistent kernel resource leak. `attach_auth_trunc()` can allocate `x->aalg`, then `attach_auth()` overwrites the pointer, so the first allocation is lost. * +1 Sustained resource exhaustion concern. Repeated XFRM state construction with the affected auth-trunc algorithm can accumulate leaked kernel memory. * -1 Privileged local control-plane requirement. Triggering requires XFRM state management through netlink and normally requires `CAP_NET_ADMIN`, but host-admin-equivalent scope is not fully established from the supplied input. Paranoid signals: * +1 Concrete persistent kernel resource leak. * +1 Sustained resource exhaustion concern. * 0 No host-admin penalty in the paranoid score because XFRM is namespace-aware and the exact capability namespace / user namespace reachability is unresolved. Important non-awarded signals: * No UAF or stale post-lifetime object use is established. * No repeated release or refcount mutation is established. * No controlled reclaim, arbitrary write, OOB access, type confusion, or callback control is established. * No confidentiality or integrity impact is awarded. * No direct network reachability is established. Remote IPsec traffic does not create the leaking state by itself. * No extra availability point is awarded beyond sustained resource exhaustion concern. * Manual review is not required because this is a resource leak without memory corruption or security-boundary bypass. Repeated-release/refcount checklist: * First release can end lifetime: not applicable. * Exact same reference survives for second lifetime mutation: no. * Second operation is real lifetime/refcount mutation: no. * Concrete repeated release/refcount +1 awarded: no. * Paranoid repeated-refcount leverage +1 awarded: no. * FLOOR 5 applied: no. ## 3. Reachability analysis The trigger is local XFRM netlink control-plane configuration, not packet data-plane processing. An attacker would need to create or modify XFRM state with an auth-trunc algorithm such as `cmac(aes)` where `attach_auth_trunc()` allocates `x->aalg` but leaves `props.aalgo` as zero. XFRM state management normally requires `CAP_NET_ADMIN`. The supplied evidence does not prove that host `CAP_NET_ADMIN` is always required, because XFRM is per-network-namespace aware. It also does not prove that an ordinary unprivileged user can complete the full trigger in an attacker-created user and network namespace on the evaluated system. Therefore `HostAdminRequired=UNKNOWN` and `NamespaceScopedPrivilege=UNKNOWN`. No prior remote setup or special hardware is required. Crypto algorithm availability may depend on kernel crypto configuration or modules, but this is not a rare hardware prerequisite. There is no race requirement. The issue is repeatable through repeated local configuration operations. ## 4. Primitive and severity interpretation The exact primitive is a persistent kernel memory leak caused by losing ownership of the first `x->aalg` allocation. The state check used `!x->props.aalgo` as a proxy for whether an auth algorithm was attached, but that proxy fails when the selected algorithm has no `sadb_alg_id`. The later `attach_auth()` call can overwrite the existing `x->aalg` pointer, and normal failure or teardown frees only the replacement pointer. This is not an active structured UAF, not fixed stale storage, and not a cleanup/destructor stale dereference. It is also not a concrete second release/refcount mutation. The demonstrated consequence is possible memory exhaustion after repeated operations. Stronger consequences such as privilege escalation, information disclosure, or arbitrary kernel corruption are speculative and not supported by the patch context. PrimitiveClass is `NONE` because no meaningful corruption, post-lifetime use, ownership-boundary bypass, or authorization primitive is established. ImportantCandidate is `NO` because this is a leak-only resource management issue. AutoDowngradeAllowed is `YES` because no unresolved memory corruption or security-boundary primitive remains. Likely operational severity is Low to ordinary Moderate, depending on whether untrusted users can manage XFRM state in namespaces or delegated environments. ## 5. One-sentence report phrase An XFRM auth-trunc allocation can be leaked during local XFRM state construction when `x.aalg` is overwritten after `props.aalgo` remains zero, allowing possible denial of service through repeated kernel memory leaks but not indicating memory corruption or privilege escalation. ## 6. Manual review recommendation NO MANUAL CHECK NEEDED The patch establishes a concrete memory leak only, with no UAF, repeated refcount mutation, authorization bypass, controlled corruption, or direct network trigger. ## 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: xfrm: fix xfrm_state_construct() auth-trunc leak Commit: 958ae9f261319e1cdc44879886bcda2263258cca Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=958ae9f261319e1cdc44879886bcda2263258cca Commit description: attach_auth_trunc() can allocate x->aalg while leaving x->props.aalgo at zero when the selected auth algorithm has no sadb_alg_id. One real case is cmac(aes). xfrm_state_construct() then treats !x->props.aalgo as "no auth algorithm attached yet" and calls attach_auth(). That overwrites x->aalg and loses the first allocation. Any later failure or teardown only frees the replacement pointer. Check whether x->aalg is already attached instead of inferring that state from x->props.aalgo. Fixes: 4447bb3 ("xfrm: Store aalg in xfrm_state with a user specified truncation length") Cc: stable@vger.kernel.org Reported-by: Vega Assisted-by: Codex:gpt-5.4 Signed-off-by: Zihan Xi Signed-off-by: Ren Wei Signed-off-by: Steffen Klassert Signed-off-by: Greg Kroah-Hartman Changed files: net/xfrm/xfrm_user.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=958ae9f261319e1cdc44879886bcda2263258cca ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80843 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80843 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:H/UI:N/S:U/C:N/I:N/A:L The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 5.5 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: 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).