From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-52936][LOW] crypto: jitterentropy - replace long-held spinlock with mutex [ Upstream Date: Wed, 24 Jun 2026 04:38:01 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-52936 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: 18216b8ab6904753eaf31baf453cb02ecd202ba4 List-Id: CVE: CVE-2026-52936 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: crypto: jitterentropy - replace long-held spinlock with mutex [ Upstream Commit: 18216b8ab6904753eaf31baf453cb02ecd202ba4 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=18216b8ab6904753eaf31baf453cb02ecd202ba4 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52936 Analysis date: Wed, 24 Jun 2026 04:38:01 -0400 ActionableScore: 2 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate / Low-like Manual review required: NO Summary: A local contention issue in jitterentropy can cause CPU stalls because a spinlock is held across expensive entropy generation, but the patch shows a DoS-only synchronization fix without memory corruption or privilege escalation evidence. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-52936 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52936 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-2026-52936 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:N/A:H';**CWE-400;CWE-667;CWE-662;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'jitterentropy RNG used a spinlock while running expensive entropy collection and SHA3 conditioning inside jent_read_entropy. Parallel local readers can contend on the same shared state and spin while the lock holder performs slow work, which can cause CPU stalls and denial of service through degraded system responsiveness. For the CVSS the PR:L value is used because a local user or local process context is needed to drive repeated RNG requests, while no administrative privilege is normally implied by the bug class itself. The issue is not network reachable and there is no evidence of memory corruption, information disclosure, or privilege escalation. Impact is denial of service only, with the paranoid score using A:H only for sustained contention that can realistically cause severe availability loss.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) YES LOCK DANGER INIT SIMPLEFIX LINUS DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 NO NO 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 process may be able to drive repeated RNG requests through normal local crypto interfaces when jitterentropy is available. * Availability impact realistic: +1 Parallel readers can spin on a long-held spinlock while entropy collection and SHA3 conditioning run, causing CPU stalls or degraded responsiveness. * No memory corruption: +0 The patch only changes locking from spinlock to mutex. It does not show UAF, OOB access, double-free, stale pointer reuse, type confusion, or arbitrary write. * No privilege escalation plausible: +0 There is no reclaim, overwrite, callback, refcount, or object-confusion primitive. * Not network reachable: +0 The path is local/control-plane style crypto API usage, not packet parsing or remote protocol handling. * No strong DoS bonus: +0 The commit describes stalls from spinning, not a reliable kernel panic, persistent crash, or filesystem/data corruption. ## 3. Reachability analysis The likely trigger is a local process or local kernel consumer issuing parallel requests to the jitterentropy RNG. No administrative privilege is clearly required by the bug class itself, but practical reachability depends on whether the jitterentropy crypto RNG is available through local crypto interfaces such as AF_ALG or used by local workloads. Namespaces do not materially change the impact unless they expose the same crypto API to untrusted tenants. This is not remotely reachable and does not involve firmware, DMA, networking, or filesystem metadata paths. ## 4. Severity interpretation This behaves like an ordinary Moderate or Low-like local availability issue. The realistic impact is CPU stall or responsiveness degradation from spinning on a lock held across expensive entropy generation. The theoretical impact does not extend to memory corruption or privilege escalation based on this patch, because the fix does not address object lifetime, bounds, ownership, pointer reuse, or write primitives. ## 5. One-sentence report phrase A local contention issue in jitterentropy can cause CPU stalls because a spinlock is held across expensive entropy generation, but the patch shows a DoS-only synchronization fix without memory corruption or privilege escalation evidence. ## 6. Manual review recommendation NO MANUAL CHECK NEEDED Reason: DoS-only locking/resource-consumption issue, no network exposure, no memory corruption primitive, no sensitive boundary bypass, and ActionableScore is below the manual-review threshold. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: crypto: jitterentropy - replace long-held spinlock with mutex [ Upstream Commit: 18216b8ab6904753eaf31baf453cb02ecd202ba4 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=18216b8ab6904753eaf31baf453cb02ecd202ba4 Changed files: crypto/jitterentropy-kcapi.c crypto/internal/rng.h 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=18216b8ab6904753eaf31baf453cb02ecd202ba4 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-52936 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52936 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: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: 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).