From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-53391][MODERATE 7.0] NFSv4/pNFS: reject zero-length r_addr in nfs4_decode_mp_ds_addr Date: Sun, 19 Jul 2026 11:06:13 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-53391 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: unknown X-AL-KERNEL-Commit: 76b94cbd32aacf36a641956385a852635c6802b9 List-Id: CVE: CVE-2026-53391 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: NFSv4/pNFS: reject zero-length r_addr in nfs4_decode_mp_ds_addr Commit: 76b94cbd32aacf36a641956385a852635c6802b9 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=76b94cbd32aacf36a641956385a852635c6802b9 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53391 Analysis date: Sun, 19 Jul 2026 11:06:13 -0400 ActionableScore: 5 ActionableScore lower bound: unknown Actionable bucket: Actionable Moderate at minimum Manual review required: YES Summary: A malicious or compromised NFSv4 pNFS metadata server can return a zero-length r_addr or r_netid in GETDEVICEINFO, causing nfs4_decode_mp_ds_addr() to dereference NULL and crash the client kernel. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53391 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53391 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: YES A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-53391 MODERATE CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';**CWE-476;*CWE-20;CWE-754;BEST CVSS score: '7.5';DESCR 'A NULL pointer dereference in the NFSv4 pNFS client path can occur because nfs4_decode_mp_ds_addr accepts zero length r_netid or r_addr values returned in a GETDEVICEINFO multipath data server response. xdr_stream_decode_string_dup can return 0 while leaving the decoded string pointer NULL, and the next parsing step may call strrchr on that NULL pointer. A malicious or compromised NFS metadata server can trigger this against a pNFS flexfile client by returning a malformed GETDEVICEINFO body, causing a kernel crash on the client. For the CVSS the PR:N because the attacker does not need local privileges on the victim host and only needs control of or network position over the metadata server endpoint used by the client. The issue is network reachable in NFS deployments, although NFS and pNFS are typically deployed inside trusted storage or data center networks rather than exposed to the public Internet. Impact is denial of service only because the patch supports a NULL pointer dereference and does not show a UAF, OOB write, information leak, or arbitrary write primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5) YES DANGER NULLPTR DISK SIMPLEFIX NETWORK LINUS IPV6 KPANIC KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ## 1. ActionableScore * Conservative score: 5 * Paranoid score: 5 * Final recommended bucket: **Actionable Moderate at minimum** ## 2. Signal breakdown * Remote reachable / network-triggerable: +2 A malicious or compromised NFS metadata server can return a malformed GETDEVICEINFO response to a mounted pNFS flexfile client. * Reliable kernel crash / strong DoS: +1 Zero-length r_addr or r_netid can leave the decoded pointer NULL, followed by strrchr(NULL, '.') in kernel context. * Availability impact realistic: +1 The commit explicitly describes client panic rather than a harmless validation failure. * Important filesystem/storage path: +1 This is in the NFSv4/pNFS client storage path and affects handling of server-provided layout/device information. Not counted: * Generic memory corruption: +0 The patch supports NULL pointer dereference only, not UAF, OOB write, double free, refcount misuse, or type confusion. * Privilege escalation plausible: +0 No reclaim, overwrite, callback, object replacement, or arbitrary write primitive is shown. * Confidentiality / integrity impact: +0 No information disclosure or data modification primitive is evident. ## 3. Reachability analysis The bug is triggerable by a malicious or compromised NFS metadata server, or by an attacker able to tamper with the server response path. The victim must be an NFSv4 pNFS flexfile client mounted against that server. No local privileges are required on the victim host, but practical exposure is usually limited to storage or data-center networks rather than the public Internet. Containers and namespaces do not materially reduce the attacker requirement unless they can cause the host to mount or communicate with an attacker-controlled pNFS server. Call-site confidence: high, because the commit describes the exact decode path and the immediate NULL dereference sink. ## 4. Severity interpretation This behaves like an actionable Moderate remote DoS issue, not an Important-class memory corruption issue. The network-triggerable crash makes it unsuitable for automatic low-priority closure, but the demonstrated primitive is a NULL pointer dereference only. There is no evidence of UAF, attacker-controlled memory reuse, arbitrary write, info leak, or privilege escalation. ## 5. One-sentence report phrase A malicious or compromised NFSv4 pNFS metadata server can return a zero-length r_addr or r_netid in GETDEVICEINFO, causing nfs4_decode_mp_ds_addr() to dereference NULL and crash the client kernel. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: the issue is network-triggerable from a malicious or compromised storage server and can crash the kernel client, but review should confirm deployment exposure because impact is DoS-only and limited to pNFS-capable NFS client configurations. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: NFSv4/pNFS: reject zero-length r_addr in nfs4_decode_mp_ds_addr Commit: 76b94cbd32aacf36a641956385a852635c6802b9 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=76b94cbd32aacf36a641956385a852635c6802b9 Commit description: nfs4_decode_mp_ds_addr() decodes the r_netid and r_addr opaques of a netaddr4 from a GETDEVICEINFO multipath-DS body, then immediately calls strrchr(buf, '.') to locate the port separator. Both decodes use xdr_stream_decode_string_dup(), and the current code checks only "nlen < 0" / "rlen < 0" before dereferencing the returned string. When the on-wire opaque has length zero, xdr_stream_decode_opaque_inline() returns 0 and xdr_stream_decode_string_dup() falls through to its "*str = NULL; return ret" tail, leaving buf NULL with a return value of 0. The "< 0" check does not catch this, and the next line is strrchr(NULL, '.'), a kernel NULL pointer dereference reachable from any pNFS-flexfile client mounted against a malicious or compromised metadata server. Reject the zero-length cases explicitly so the decoder fails with -EBADMSG (treated as a malformed GETDEVICEINFO body) instead of panicking the client. Cc: stable@vger.kernel.org Fixes: 6b7f3cf ("nfs41: pull decode_ds_addr from file layout to generic pnfs") Assisted-by: Claude:claude-opus-4-7 Signed-off-by: Michael Bommarito Signed-off-by: Anna Schumaker Signed-off-by: Greg Kroah-Hartman Changed files: fs/nfs/pnfs_nfs.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=76b94cbd32aacf36a641956385a852635c6802b9 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53391 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53391 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:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 7.5 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: 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).