From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-45842][MODERATE REGULAR] slip: reject VJ receive packets on instances with no rstate array [ Upstream Date: Wed, 27 May 2026 06:12:24 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-45842 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: 2 X-AL-KERNEL-Commit: c6980e8b1a86288167f34966fa5219031999b6f1 List-Id: CVE: CVE-2026-45842 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: slip: reject VJ receive packets on instances with no rstate array [ Upstream Commit: c6980e8b1a86288167f34966fa5219031999b6f1 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c6980e8b1a86288167f34966fa5219031999b6f1 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45842 Analysis date: Wed, 27 May 2026 06:12:24 -0400 ActionableScore: 3 ActionableScore lower bound: 2 Actionable bucket: Borderline, manual review recommended Manual review required: YES Summary: A malformed PPP VJ compression configuration can leave SLHC receive state without an `rstate` array, allowing a local namespace-capable attacker to trigger a NULL pointer dereference and kernel crash with a slot 0 VJ receive frame. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-45842 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45842 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-2026-45842 MODERATE 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-476;*CWE-20;CWE-754;BEST CVSS score: '5.5';DESCR 'SLIP VJ receive handling can dereference a NULL rstate array when PPP creates an slhc instance with zero receive slots. A local user can reach the configuration path through PPPIOCSMAXCID in an unprivileged user namespace when CAP_NET_ADMIN is available there and /dev/ppp is accessible. After that, an inbound VJ compressed or VJ uncompressed frame selecting slot 0 can crash the kernel in softirq context. For the CVSS the PR:L is used because the attacker needs local code execution and namespace or PPP access, but not full host root in systems with unprivileged user namespaces. The issue is a NULL pointer dereference and not a use after free or write primitive. Impact is denial of service via kernel crash only.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 3) YES KASAN OOB NULLPTR NETWORK KERNEL_PANIC_PLUS_UAF PACKET DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=3 ActionableScoreLower=2 ## 1. ActionableScore * Conservative score: 2 * Paranoid score: 3 * Final recommended bucket: **Borderline, manual review recommended**:: ## 2. Signal breakdown Conservative signals: * Local trigger through namespace or PPP setup: +1. The commit states that `PPPIOCSMAXCID` can lead to `slhc_init(0, 1)` and that `/dev/ppp` is gated by `ns_capable(CAP_NET_ADMIN)`, making the path reachable from an unprivileged user namespace on affected systems. * Reliable kernel crash / strong DoS: +1. A VJ-compressed or VJ-uncompressed frame selecting slot 0 dereferences `comp->rstate` when it is NULL and crashes the kernel in softirq context. * Availability impact realistic: +1. The demonstrated result is a kernel general protection fault / NULL pointer dereference. * Rare or configuration-dependent path: -1. The issue requires PPP/SLIP VJ compression state and access to `/dev/ppp`, so it is not a broad default networking path. Conservative total: 2. Paranoid additional interpretation: * Cross-boundary isolation concern: +1. If an unprivileged user namespace can configure the malformed PPP VJ state and crash the host kernel, this is more important than a normal privileged local DoS. Paranoid total: 3. No memory corruption signal is counted. The patch supports NULL pointer dereference only, not UAF, OOB write, arbitrary write, refcount corruption, or a credible LPE primitive. ## 3. Reachability analysis The attacker needs local execution and access to `/dev/ppp` with `CAP_NET_ADMIN` in the relevant namespace. The commit explicitly notes that this can be reachable from an unprivileged user namespace because the PPP open path uses `ns_capable(CAP_NET_ADMIN)`. After the malformed SLHC receive state is installed, an inbound VJ-compressed or VJ-uncompressed frame selecting slot 0 can trigger the crash. This is not remotely Internet-triggerable by itself. It depends on PPP/SLIP VJ compression configuration and on the ability to create or influence a PPP receive path. The affected subsystem is relatively uncommon, but the demonstrated crash path is direct once the setup exists. ## 4. Severity interpretation This behaves like a local namespace-reachable DoS, not an Important-class memory corruption vulnerability. The realistic impact is kernel crash. The theoretical memory-corruption or privilege-escalation potential is weak because the primitive is a NULL `rstate` dereference and the fix only adds NULL checks before receive processing. It should not be auto-treated as high severity, but manual review is reasonable because the commit explicitly highlights unprivileged user namespace reachability and a host kernel crash. ## 5. One-sentence report phrase A malformed PPP VJ compression configuration can leave SLHC receive state without an `rstate` array, allowing a local namespace-capable attacker to trigger a NULL pointer dereference and kernel crash with a slot 0 VJ receive frame. ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED. Reason: the issue is DoS-only and not memory corruption, but the stated unprivileged user namespace reachability makes it more actionable than a normal CAP_NET_ADMIN-only crash. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: slip: reject VJ receive packets on instances with no rstate array [ Upstream Commit: c6980e8b1a86288167f34966fa5219031999b6f1 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c6980e8b1a86288167f34966fa5219031999b6f1 Changed files: drivers/net/slip/slhc.c drivers/net/ppp/ppp_generic.c drivers/net/ppp/ppp_async.c kernel/softirq.c kernel/smpboot.c kernel/kthread.c arch/x86/kernel/process.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=c6980e8b1a86288167f34966fa5219031999b6f1 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-45842 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45842 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: Not available 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: 2 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).