From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74611][IMPORTANT] tls: rx: restore msg_iter before TLS 1.3 optimistic retry Date: Sat, 22 Aug 2026 13:00:58 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74611 X-AL-KERNEL-Priority: IMPORTANT X-AL-KERNEL-Severity: IMPORTANT X-AL-KERNEL-Base-Severity: IMPORTANT X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 6 X-AL-KERNEL-ActionableScore-Lower: 5 X-AL-KERNEL-Commit: 68787940274ec89f41dc91b1a68ee1a16a90735f List-Id: CVE: CVE-2026-74611 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: tls: rx: restore msg_iter before TLS 1.3 optimistic retry Commit: 68787940274ec89f41dc91b1a68ee1a16a90735f Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=68787940274ec89f41dc91b1a68ee1a16a90735f Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74611 Analysis date: Sat, 22 Aug 2026 13:00:58 -0400 ActionableScore: 6 ActionableScore lower bound: 5 Actionable bucket: Actionable Moderate at minimum Manual review required: YES Summary: A remote TLS peer can trigger a kTLS TLS 1.3 RX retry bug that leaves msg_iter advanced, causing decrypted bytes to be written into later user iovecs beyond the length reported by recvmsg(). ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74611 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74611 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: IMPORTANT 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-2026-74611 IMPORTANT CHECK WITH IMPACT FROM ORIG NN IMPORTANT Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:L';*CWE-787;CWE-119;*CWE-20;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '7';DESCR 'A user buffer overwrite can occur in the TLS 1.3 RX path because tls_decrypt_sg advances msg_iter for the optimistic zero-copy path and tls_decrypt_sw retries through an skb without restoring the iterator. A remote TLS peer can trigger this after the receiver enables TLS_RX_EXPECT_NO_PAD by sending a record that forces the optimistic path to retry, causing decrypted bytes to be copied into later caller iovecs beyond the length reported by recvmsg(). For the CVSS the PR:N because the attacker does not need local code execution or an account on the receiver and only needs network access to the affected TLS connection. The issue is network reachable but depends on a specific kTLS TLS 1.3 receive configuration, so AC:H is used. Impact is at least integrity corruption of receiver user buffers and possible application level denial of service. In the paranoid interpretation, limited confidentiality and high integrity impact are kept for manual review sensitivity, but this is not classified as kernel memory corruption or proven privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 7) YES REMOTE INIT SKB LINUS KPANIC YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=6 ActionableScoreLower=5 ## 1. ActionableScore * Conservative score: 5 * Paranoid score: 6 * Final recommended bucket: **Actionable Moderate at minimum**:: ## 2. Signal breakdown Triggered signals: * Remote reachable / network-triggerable: +2 A TLS peer can trigger the condition by sending a TLS 1.3 record that forces the optimistic RX zero-copy path to retry. * Constrained overwrite / weak corruption candidate: +1 The overwrite is into caller supplied user iovecs, not kernel memory. It is still security relevant because the kernel writes decrypted bytes beyond the length reported by recvmsg(). * Memory layout invariant restoration: +1 The patch restores consistency of msg_iter after optimistic zero-copy mapping before retrying through skb. * Integrity impact plausible: +1 A peer can cause unexpected modification of later user buffers in the receiving application. * Practical exploit chain demonstrated or strongly implied: +1 The added selftest directly demonstrates the out-of-position iovec overwrite condition. Subtracted signals: * Rare AND difficult-to-reach subsystem/configuration: -1 The issue requires kTLS RX, TLS 1.3, optimistic zero-copy behavior, and TLS_RX_EXPECT_NO_PAD enabled. Paranoid-only signal: * Availability impact realistic: +1 Application state corruption may plausibly cause application-level DoS, although this is not a demonstrated kernel crash. Not awarded: * Generic kernel memory corruption: +0 The patch shows user buffer corruption, not UAF, OOB write to kernel memory, arbitrary write, or object lifetime corruption. * Privilege escalation plausible: +0 No supported LPE primitive is shown. * Confidentiality impact: +0 conservative The peer controls the transmitted plaintext. A victim data disclosure primitive is not demonstrated. ## 3. Reachability analysis A remote authenticated or connected TLS peer can trigger the bug if the receiver uses kTLS RX with TLS 1.3 and enables TLS_RX_EXPECT_NO_PAD. No local account on the receiver is required, so the practical PR is PR:N in CVSS terms. The affected path is not a default generic TCP receive path because it depends on kTLS RX options and the optimistic zero-copy retry path. Containers and namespaces are not the main privilege boundary here because the trigger is over an established TLS connection to an application using the affected kTLS configuration. Call-site confidence: high. The patch and selftest show the relevant tls_decrypt_sw retry path and the resulting recvmsg iovec overwrite behavior. ## 4. Severity interpretation This is more than an ordinary Moderate because it is network-triggerable and causes a kernel-mediated overwrite of receiver application buffers beyond the returned recvmsg length. It does not currently look like Important-class kernel memory corruption because the overwrite target is user iovec memory selected by the receiving process, not attacker-selected kernel memory. The realistic impact is application memory integrity corruption and possible application DoS under a specific kTLS TLS 1.3 configuration. The paranoid score keeps it actionable because remote input can violate recvmsg buffer semantics. ## 5. One-sentence report phrase A remote TLS peer can trigger a kTLS TLS 1.3 RX retry bug that leaves msg_iter advanced, causing decrypted bytes to be written into later user iovecs beyond the length reported by recvmsg(). ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: the issue is network reachable and the selftest demonstrates a real user buffer overwrite beyond the reported recvmsg length, even though it is not proven kernel memory corruption or privilege escalation. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: tls: rx: restore msg_iter before TLS 1.3 optimistic retry Commit: 68787940274ec89f41dc91b1a68ee1a16a90735f Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=68787940274ec89f41dc91b1a68ee1a16a90735f Commit description: tls_decrypt_sg() advances msg->msg_iter when it maps user pages for the optimistic TLS 1.3 zero-copy path. If the decrypted record turns out not to be unpadded application data, tls_decrypt_sw() retries into a kernel skb, but leaves the iterator advanced. The subsequent copy from the skb then writes decrypted bytes again at a later point in the caller iovecs while recvmsg() reports only the post-retry length. A TLS peer can trigger this after the receiver enables TLS_RX_EXPECT_NO_PAD. Revert the iterator by the number of bytes consumed by the optimistic mapping before retrying without zero-copy. Add a selftest which sends a TLS 1.3 control record with TLS_RX_EXPECT_NO_PAD enabled and verifies that recvmsg() does not overwrite later iovecs beyond the returned length. Fixes: ce61327 ("tls: rx: support optimistic decrypt to user buffer with TLS 1.3") Cc: stable@vger.kernel.org Signed-off-by: Jérémy Jean Link: https://patch.msgid.link/20260804125528.2139928-1-Jeremy.Jean@oss.cyber.gouv.fr Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman Changed files: net/tls/tls_sw.c tools/testing/selftests/net/tls.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=68787940274ec89f41dc91b1a68ee1a16a90735f ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74611 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74611 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:L/A:L The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:L The Best / paranoid CVSS score: 7 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: 5 Paranoid ActionableScore: 6 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: IMPORTANT KPANIC detected for this report: YES Published priority for this report (same as in Subject): IMPORTANT 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).