From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-53176][IMPORTANT] IB/isert: Reject login PDUs shorter than ISER_HEADERS_LEN Date: Mon, 06 Jul 2026 16:45:34 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-53176 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: 8 X-AL-KERNEL-ActionableScore-Lower: 6 X-AL-KERNEL-Commit: 75ee6e4aa096aa9e7b2dd5c8ff98356e30aceefb List-Id: CVE: CVE-2026-53176 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: IB/isert: Reject login PDUs shorter than ISER_HEADERS_LEN Commit: 75ee6e4aa096aa9e7b2dd5c8ff98356e30aceefb Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=75ee6e4aa096aa9e7b2dd5c8ff98356e30aceefb Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53176 Analysis date: Mon, 06 Jul 2026 16:45:34 -0400 ActionableScore: 8 ActionableScore lower bound: 6 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A pre-auth iSER target login length underflow can turn a short remote login PDU into a multi-gigabyte memcpy length, causing an out-of-bounds kernel write and reliable target crash, with paranoid concern for broader memory corruption impact. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53176 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53176 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-2026-53176 IMPORTANT CHECK WITH IMPACT FROM ORIG NN IMPORTANT Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H';CWE-191;*CWE-787;*CWE-20;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '8.8';DESCR 'An out of bounds memcpy in the iSER target login path can occur because isert_login_recv_done subtracts ISER_HEADERS_LEN from wc byte_len without first checking the lower bound. A remote iSER initiator can send a login Send work request shorter than ISER_HEADERS_LEN before iSCSI authentication, making login_req_len negative and later sign extended into a very large memcpy length for the 8192 byte login req_buf. For the CVSS the PR:N is selected because the affected path is reachable before iSCSI credentials are required when the iSER target is exposed to the initiator. The issue is network reachable on an RDMA or storage fabric rather than a normal local syscall path. Impact is at least denial of service via target kernel crash and in the paranoid case may allow confidentiality or integrity impact due to an out of bounds kernel write primitive. iSER targets are typically deployed in isolated data center storage networks, so practical exploitation usually requires access to the trusted RDMA fabric rather than the public Internet.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8) YES OOB DANGER NETWORK KERNEL_PANIC_PLUS_UAF KPANIC NO NO guess ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=8 ActionableScoreLower=6 ## 1. ActionableScore * Conservative score: 6 * Paranoid score: 8 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative signals: * Remote reachable / network-triggerable: +2. A remote iSER initiator can reach the login path over an RDMA or storage fabric before iSCSI authentication. * Generic memory corruption, strong corruption primitive: +2. The signed underflow can become a very large memcpy size, causing an out-of-bounds kernel write into and beyond login->req_buf. * Reliable kernel crash / strong DoS: +1. The described practical result is a target kernel fault and crash. * Important filesystem/storage path: +1. This is in the iSER target login path for remote storage access. * Rare AND difficult-to-reach subsystem/configuration: -1. iSER is not a default Internet-facing service and is usually limited to RDMA/storage networks. * Availability impact realistic: +1. The crash is pre-auth and appears easy to trigger once the target fabric is reachable. Paranoid additional signals: * Confidentiality impact plausible: +1. Kernel out-of-bounds copy behavior may expose or corrupt adjacent kernel memory in less deterministic cases. * Integrity impact plausible: +1. The primitive is an out-of-bounds kernel write, even if practical exploitation is more likely to crash than to provide controlled corruption. ## 3. Reachability analysis The bug is reachable by a remote iSER initiator that can connect to the target over the RDMA or storage fabric. No iSCSI credentials are required because the vulnerable path is in the login phase before authentication. This is not a typical public Internet remote attack surface, but it is realistically network-triggerable inside data-center, storage, or RDMA fabrics. Namespaces do not materially reduce the attacker requirement on the target side because the trigger is remote protocol input, not a local syscall requiring host privileges. Call-site confidence: high. The commit message describes the downstream path from isert_login_recv_done() to isert_rx_login_req() and then to memcpy() with the sign-extended negative length. ## 4. Severity interpretation This is stronger than an ordinary Moderate issue because it is pre-auth, remotely reachable on the relevant storage fabric, and involves a concrete out-of-bounds memcpy in kernel target code. Realistic exploitation evidence points most strongly to reliable DoS through target kernel crash. Theoretical worst-case impact is higher because the bug is not merely a NULL dereference or validation warning, but a real kernel memory corruption primitive, although controlled privilege escalation or code execution is not demonstrated. ## 5. One-sentence report phrase A pre-auth iSER target login length underflow can turn a short remote login PDU into a multi-gigabyte memcpy length, causing an out-of-bounds kernel write and reliable target crash, with paranoid concern for broader memory corruption impact. ## 6. Manual review recommendation MANUAL CHECK REQUIRED. This is pre-auth network-reachable kernel memory corruption in a storage target path, so it should not be auto-closed even if the most reproducible impact is DoS. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: IB/isert: Reject login PDUs shorter than ISER_HEADERS_LEN Commit: 75ee6e4aa096aa9e7b2dd5c8ff98356e30aceefb Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=75ee6e4aa096aa9e7b2dd5c8ff98356e30aceefb Commit description: In drivers/infiniband/ulp/isert/ib_isert.c, isert_login_recv_done() computes the login request payload length as wc->byte_len minus ISER_HEADERS_LEN with no lower bound, and login_req_len is a signed int. A remote iSER initiator can post a login Send work request carrying fewer than ISER_HEADERS_LEN (76) bytes, so the subtraction underflows and login_req_len becomes negative. isert_rx_login_req() then reads that negative length back into a signed int, takes size = min(rx_buflen, MAX_KEY_VALUE_PAIRS), and because the min() is signed it keeps the negative value; the value is then passed as the memcpy() length and sign-extended to a multi-gigabyte size_t. The copy into the 8192-byte login->req_buf runs far out of bounds and faults, crashing the target node. The login phase precedes iSCSI authentication, so no credentials are required to reach this path. Reject any login PDU shorter than ISER_HEADERS_LEN before the subtraction, mirroring the existing early return on a failed work completion, so login_req_len can never go negative. The upper bound was already safe: a posted login buffer cannot deliver more than ISER_RX_PAYLOAD_SIZE, so the difference stays at or below MAX_KEY_VALUE_PAIRS and the existing min() clamps it; only the missing lower bound needs to be added. Fixes: b8d26b3 ("iser-target: Add iSCSI Extensions for RDMA (iSER) target driver") Link: https://patch.msgid.link/r/20260602194642.2273217-1-michael.bommarito@gmail.com Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Michael Bommarito Signed-off-by: Jason Gunthorpe Signed-off-by: Greg Kroah-Hartman Changed files: drivers/infiniband/ulp/isert/ib_isert.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=75ee6e4aa096aa9e7b2dd5c8ff98356e30aceefb ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53176 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53176 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:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 8.8 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: 6 Paranoid ActionableScore: 8 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).