CVE-2026-23364

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This is a timing side-channel attack requiring many network requests to statistically distinguish memcmp() early-return timing differences; network jitter is beyond the attacker's control and adds noise that significantly increases exploitation difficulty.\nPR:N - The most critical vulnerable comparison (NTLMv2 MAC in ksmbd_auth_ntlmv2) is reached during the SMB session setup authentication handshake, before any credentials are verified \u2014 no prior privileges are needed.\nUI:N - The attacker directly sends SMB authentication requests to the ksmbd server; no victim user action is required.\nS:U - The vulnerability and its impact remain within the ksmbd/kernel security authority; no security boundary is crossed.\nC:H - Successful timing attack on the NTLMv2 MAC comparison enables authentication bypass, granting the attacker full read access to all SMB-shared files and data.\nI:H - Authentication bypass via forged NTLMv2 response grants write access to SMB shares, allowing arbitrary modification of shared data.\nA:N - 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{"bugzilla": {"description": "kernel: ksmbd: Compare MACs in constant time", "id": "2451167", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2451167"}, "csaw": false, "cwe": "CWE-208", "details": ["A flaw was found in ksmbd, a Linux kernel module. This vulnerability stems from the use of a non-constant time memory comparison function when verifying Message Authentication Codes (MACs). A remote attacker could exploit this timing difference to conduct a timing attack, potentially leading to the disclosure of sensitive information."], "name": "CVE-2026-23364", "package_state": [{"cpe": "cpe:/o:redhat:enterprise_linux:10", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 10"}, {"cpe": "cpe:/o:redhat:enterprise_linux:6", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 6"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Not affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Not affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 9"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Not affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 9"}], "public_date": "2026-03-25T00:00:00Z", "references": ["https://www.cve.org/CVERecord?id=CVE-2026-23364\nhttps://nvd.nist.gov/vuln/detail/CVE-2026-23364\nhttps://lore.kernel.org/linux-cve-announce/2026032539-CVE-2026-23364-4267@gregkh/T"]}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "code_commit", "value": "[e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9,cd52a0e309659537048a864211abc3ea4c5caa63)"}}, {"platform": null, "status": "affected", "versions": {"scheme": "code_commit", "value": "[e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9,307afccb751f542246bd5dc68a2c1ffe1a78418c)"}}, {"platform": null, "status": "affected", "versions": {"scheme": "code_commit", "value": "[e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9,2cdc56ed67615ba0921383a688f24415ebe065f3)"}}, {"platform": null, "status": "affected", "versions": {"scheme": "code_commit", "value": "[e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9,93c0a22fec914ec4b697e464895a0f594e29fb28)"}}, {"platform": null, "status": "affected", "versions": {"scheme": "code_commit", "value": "[e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9,f4588b85efd6007d46b80aa1b9fb746628ffb3dc)"}}, {"platform": null, "status": "affected", "versions": {"scheme": "code_commit", "value": "[e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9,c5794709bc9105935dbedef8b9cf9c06f2b559fa)"}}], "enrichment": {"confidence": 99.0, "confidence_source": "inferred", "scores": [{"score": 99.0, "source": "inferred"}, {"score": 100.0, "source": "matching"}]}, "original": {"product": "Linux", "source": "cna", "vendor": "Linux"}, "product": "linux_kernel", "vendor": "linux"}, {"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "generic", "value": "5.15"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "[0,5.15)"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "[6.1.167,7.0.0)"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "[6.6.130,7.0.0)"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "[6.12.78,7.0.0)"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "[6.18.19,7.0.0)"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "[6.19.7,7.0.0)"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "generic", "value": "[7.0-rc2,*]"}}], "enrichment": {"confidence": 99.0, "confidence_source": "inferred", "scores": [{"score": 99.0, "source": "inferred"}, {"score": 100.0, "source": "matching"}]}, "original": {"product": "Linux", "source": "cna", "vendor": "Linux"}, "product": "linux_kernel", "vendor": "linux"}], "analysis": {"en": {"generated_at": "2026-04-29T01:59:46.390088+00:00", "value": {"mitigation_remediation": ["Upgrade the Linux kernel to a version that includes the crypto_memneq fix for ksmbd and reboot to activate the patched kernel.", "If a kernel upgrade cannot be performed immediately, temporarily disable the ksmbd service so that SMB traffic is not processed.", "Further reduce exposure by restricting SMB service access to trusted internal networks and applying firewall rules that block SMB connections from untrusted hosts."], "summary": {"action": "Immediate Patch", "impact": "Timing-based information disclosure that can lead to unauthorized SMB access"}, "threat_synthesis": {"affected_systems": "The vulnerability applies to all Linux kernels that include the ksmbd code before the patch that replaces memcmp with the constant\u2011time function crypto_memneq. The CPE identifiers indicate affected kernels include the generic Linux kernel, Linux kernel 5.15 releases, and pre\u2011release builds of Linux 7.0 from release candidate 1 through 7. Kernels that have been updated to include the fix are no longer affected.", "description_and_impact": "The Linux kernel\u2019s ksmbd service performs verification of message authentication codes (MACs) using the generic memcmp routine. Because memcmp stops on the first differing byte, the time taken to compare two MAC values varies with the number of matching leading bytes. This timing variation can be measured by an attacker to recover the correct MAC value byte by byte, allowing them to impersonate an authenticated user on the SMB service. The vulnerability is a classic timing\u2011based information\u2011disclosure attack that, if combined with network access to the SMB service, can enable unauthorized access to shared resources. The description indicates that an attacker could measure the timing differences to deduce MAC bytes; it is inferred that this could allow an attacker to impersonate an authenticated user on SMB, but the CVE text does not explicitly confirm that the restored MAC would grant full access.", "risk_and_exploitability": "The CVSS score of 7.4 indicates a moderate\u2011to\u2011high severity vulnerability. The EPSS score of less than 1% suggests that, historically, exploitation is uncommon, and the vulnerability is not listed in the CISA KEV catalog. Based on the description, it is inferred that the attack requires the SMB service to be exposed on the network and the attacker to have the capability to measure response times with sufficient precision. If these conditions are met, the attacker could reconstruct the MAC and gain unauthorized access to SMB shares."}}}}, "created": "2026-03-25T21:31:51.736327+00:00", "updated": "2026-04-29T02:00:27.294046+00:00", "vendors": ["linux", "linux$PRODUCT$linux_kernel"]}