From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-93207][MODERATE 7.0] SUNRPC: Zero rpc_gss_wire_cred at svcauth_gss_decode_credbody() entry Date: Thu, 24 Sep 2026 12:04:13 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-93207 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: 56b29d62017c7dd1718d060dd5b3a2ce61095d0c List-Id: CVE: CVE-2026-93207 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: SUNRPC: Zero rpc_gss_wire_cred at svcauth_gss_decode_credbody() entry Commit: 56b29d62017c7dd1718d060dd5b3a2ce61095d0c Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=56b29d62017c7dd1718d060dd5b3a2ce61095d0c Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93207 Analysis date: Thu, 24 Sep 2026 12:04:13 -0400 ActionableScore: 5 ActionableScore lower bound: 4 Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-93207 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93207 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-2026-93207 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-93207 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:L/I:N/A:H';*CWE-416;CWE-665;*CWE-20;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '8.2';DESCR 'A use-after-free read condition exists in the SUNRPC RPCSEC_GSS credential decoder because a failed decode can leave stale gc_ctx length data paired with a borrowed pointer into request XDR pages. When the request pages are released and the per request credential storage is reused, a later length driven lookup such as gss_svc_searchbyctx can walk a dangling pointer. For the CVSS the PR:N in the paranoid score is selected because malformed RPCSEC_GSS traffic reaches credential decoding before successful request authentication and an attacker does not necessarily need a local account on the target. The base score uses AC:H because reliable triggering requires a specific request sequence and reuse of pooled request state. The paranoid score uses AC:L if an attacker can induce such reuse through sustained RPC request traffic. Impact is at least remote denial of service through a kernel memory safety fault. Limited confidentiality impact is plausible because stale length based processing can read released or reused request memory. Integrity impact and privilege escalation are not established because the patch shows no write primitive or control flow primitive. SUNRPC services such as NFS are commonly reachable only from trusted storage or internal networks but exposure depends on RPC service configuration.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) YES REMOTE DANGER NETWORK KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=4 PrimitiveClass=CLASS_B RealUAF=YES HostAdminRequired=NO NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO 1. ActionableScore * Raw conservative score: 4 * Conservative score: 4 * Raw paranoid score: 5 * Paranoid score: 5 * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: Conservative arithmetic: Real UAF and stale post-lifetime consumption +2. Direct network reachability to an exposed RPCSEC_GSS service +2. Paranoid arithmetic: Conservative signals +4. Attacker-influenced repeated request and request-page lifetime cycling +1. 2. Signal breakdown * +2 Real UAF or active lifetime violation. The per-request rpc_gss_wire_cred retains gc_ctx.data pointing into released XDR request pages while gc_ctx.len retains stale nonzero state. A later gss_svc_searchbyctx consumer can walk that dangling pointer. * +2 Remote reachable. Malformed RPCSEC_GSS credentials are decoded from network RPC traffic before successful request authentication. A remote sender can reach the decoder when an RPCSEC_GSS enabled SUNRPC service is exposed. * +1 paranoid only Attacker-influenced active-object state and repeatable lifetime manipulation. The sender can repeatedly submit malformed RPC requests and cause request credential decoding and request-page release cycles. This supports repeated attempts at the stale pointer and length condition. Important non-awarded signals: * Controlled reclaim or controlled replacement of the released XDR pages is not demonstrated. * Arbitrary kernel read or write is not demonstrated. * Confidentiality is not awarded. The patch establishes an invalid stale read, but no readback or network disclosure path is shown. * Integrity is not awarded. No write primitive, credential overwrite, or authorization bypass is established. * Reliable kernel crash or strong DoS is not separately awarded. Walking a dangling pointer can plausibly fault, but the supplied patch does not demonstrate a reproducible crash or panic. * Structured stale-object exploitation leverage is not separately awarded. The stale state contains an active pointer and length pair, but attacker control of post-free page reuse or of the preceding valid gc_ctx.len value is not established. * No repeated release or refcount mutation exists. The stale operation is a length-driven read or traversal, not a second put, free, or refcount decrement. 3. Reachability analysis The relevant attacker is a remote RPC client targeting an exposed SUNRPC service that uses RPCSEC_GSS, commonly an NFS server deployment. The malformed credential reaches svcauth_gss_decode_credbody before the request is successfully authenticated, so host administrator privilege is not required to submit the malformed network input. The complete trigger requires a server-side RPCSEC_GSS configuration and network exposure. This is target deployment configuration, not attacker host-admin setup. The supplied evidence does not establish whether an attacker must possess a valid GSS principal to reliably control the earlier request that supplied the stale gc_ctx.len value. That uncertainty affects reliability and exploitation control, but does not make host-admin privilege necessary. No namespace-specific capability check or namespace-contained complete trigger path is supplied. NamespaceScopedPrivilege is therefore UNKNOWN. 4. Primitive and severity interpretation The exact primitive is a use-after-free read or traversal. gc_ctx.data is a borrowed pointer into request XDR pages. On an early decode failure, gc_ctx.len can retain a prior request value. After the current request pages are released, the reused per-svc_rqst credential storage contains a dangling pointer paired with stale length data. A later consumer such as gss_svc_searchbyctx can dereference or scan the released memory. This is an active structured credential-state lifetime violation, not merely a fixed poisoned pointer that immediately faults. However, the supplied evidence establishes only stale pointer consumption through a length-driven lookup. It does not establish controlled reclaim, attacker-shaped replacement data, an arbitrary read primitive, a write primitive, callback control, credential corruption, authentication bypass, or privilege escalation. The issue is CLASS_B because a real kernel lifetime violation and post-lifetime access are concretely established. ImportantCandidate is YES because the stale pointer and stale length are consumed by later credential-context processing, and the practical behavior after page reuse requires manual exploitation review. AutoDowngradeAllowed is NO because automatically treating this as a simple parser failure would discard a network-reachable kernel UAF primitive with unresolved post-free behavior. Likely operational severity is Actionable Moderate. It can become Important if further call-site analysis shows that gss_svc_searchbyctx can disclose reused XDR contents, misidentify a security context, access unmapped memory reliably, or consume attacker-influenced reused page data. 5. One-sentence report phrase A remote RPCSEC_GSS client can cause stale credential state to retain a dangling XDR page pointer with a prior length value, allowing later context lookup code to walk released request memory and potentially cause a kernel denial of service. 6. Manual review recommendation MANUAL CHECK REQUIRED The patch directly establishes a network-reachable dangling-pointer and stale-length lifetime violation, while the reachable gss_svc_searchbyctx behavior and possible post-free page reuse effects are not fully visible. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: SUNRPC: Zero rpc_gss_wire_cred at svcauth_gss_decode_credbody() entry Commit: 56b29d62017c7dd1718d060dd5b3a2ce61095d0c Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=56b29d62017c7dd1718d060dd5b3a2ce61095d0c Commit description: svcauth_gss_decode_credbody() writes the caller's rpc_gss_wire_cred field by field and assigns gc_ctx.len only on the success tail. The caller storage is svcdata->clcred, which lives in the per-svc_rqst gss_svc_data and is reused across requests. Early decode failures leave partially decoded state mixed with residue from the prior request. The trailing body_len tightness check is the sharpest case: xdr_stream_decode_opaque_inline() has already written gc_ctx.data with a borrowed inline pointer into the current request's XDR pages, but gc_ctx.len retains its prior value. Once the request pages are released the pooled clcred carries a dangling pointer paired with a stale length. Zero the caller's rpc_gss_wire_cred at function entry so that every early-return path leaves a deterministic all-zero cred. On the trailing tightness-check path, gc_ctx.len is now zero instead of stale, which neuters length-driven consumers such as gss_svc_searchbyctx() that would otherwise walk the dangling data pointer. Fixes: b0bc534 ("SUNRPC: Convert the svcauth_gss_accept() pre-amble to use xdr_stream") Cc: stable@vger.kernel.org Signed-off-by: Chris Mason Reviewed-by: Jeff Layton Link: https://patch.msgid.link/20260528-tier2-v1-5-d026a1415e0b@oracle.com Signed-off-by: Chuck Lever Signed-off-by: Greg Kroah-Hartman Changed files: net/sunrpc/auth_gss/svcauth_gss.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=56b29d62017c7dd1718d060dd5b3a2ce61095d0c ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-93207 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93207 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:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H The Best / paranoid CVSS score: 8.2 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).