{“lastseen”:””,”description”:”Issue summary: A TLS 1.3 connection using certificate compression can be\\nforced to allocate a large buffer before decompression without checking\\nagainst the configured certificate size limit.\\n\\nImpact summary: An attacker can cause per-connection memory allocations of\\nup to approximately 22 MiB and extra CPU work, potentially leading to\\nservice degradation or resource exhaustion (Denial of Service).\\n\\nIn affected configurations, the peer-supplied uncompressed certificate\\nlength from a CompressedCertificate message is used to grow a heap buffer\\nprior to decompression. This length is not bounded by the max_cert_list\\nsetting, which otherwise constrains certificate message sizes. An attacker\\ncan exploit this to cause large per-connection allocations followed by\\nhandshake failure. No memory corruption or information disclosure occurs.\\n\\nThis issue only affects builds where TLS 1.3 certificate compression is\\ncompiled in (i.e., not OPENSSL_NO_COMP_ALG) and at least one compression\\nalgorithm (brotli, zlib, or zstd) is available, and where the compression\\nextension is negotiated. Both clients receiving a server CompressedCertificate\\nand servers in mutual TLS scenarios receiving a client CompressedCertificate\\nare affected. Servers that do not request client certificates are not\\nvulnerable to client-initiated attacks.\\n\\nUsers can mitigate this issue by setting SSL_OP_NO_RX_CERTIFICATE_COMPRESSION\\nto disable receiving compressed certificates.\\n\\nThe FIPS modules in 3.6, 3.5, 3.4 and 3.3 are not affected by this issue,\\nas the TLS implementation is outside the OpenSSL FIPS module boundary.\\n\\nOpenSSL 3.6, 3.5, 3.4 and 3.3 are vulnerable to this issue.\\n\\nOpenSSL 3.0, 1.1.1 and 1.0.2 are not affected by this issue.”,”published”:”2026-01-27T16:01:22.399Z”,”modified”:”2026-01-29T15:03:51.754Z”,”type”:”cve”,”title”:”TLS 1.3 CompressedCertificate excessive memory allocation”,”source”:”openssl”,”references”:”https:\/\/openssl-library.org\/news\/secadv\/20260127.txt\\nhttps:\/\/github.com\/openssl\/openssl\/commit\/6184a4fb08ee6d7bca570d931a4e8bef40b64451\\nhttps:\/\/github.com\/openssl\/openssl\/commit\/895150b5e021d16b52fb32b97e1dd12f20448be5\\nhttps:\/\/github.com\/openssl\/openssl\/commit\/966a2478046c311ed7dae50c457d0db4cafbf7e4\\nhttps:\/\/github.com\/openssl\/openssl\/commit\/3ed1f75249932b155eef993a8e66a99cb98bfef4″,”id”:”CVE-2025-66199″,”bulletinFamily”:””,”cwe”:[“CWE-789″],”cvelist”:null,”sourceData”:”OpenSSL OpenSSL 3.6.0\\nOpenSSL OpenSSL 3.5.0\\nOpenSSL OpenSSL 3.4.0\\nOpenSSL OpenSSL 3.3.0″,”sourceHref”:””,”cvss”:{“score”:5.9,”severity”:”MEDIUM”,”vector”:”CVSS:3.1\/AV:N\/AC:H\/PR:N\/UI:N\/S:U\/C:N\/I:N\/A:H”,”version”:”3.1″},”cvss2″:{},”cvss3″:{“version”:””,”vectorString”:””,”baseScore”:0,”baseSeverity”:””,”attackVector”:””,”attackComplexity”:””,”privilegesRequired”:””,”userInteraction”:””,”scope”:””,”confidentialityImpact”:””,”integrityImpact”:””,”availabilityImpact”:””,”cvssV3″:{“version”:””,”vectorString”:””,”baseScore”:0,”baseSeverity”:””,”attackVector”:””,”attackComplexity”:””,”privilegesRequired”:””,”userInteraction”:””,”scope”:””,”confidentialityImpact”:””,”integrityImpact”:””,”availabilityImpact”:””}},”href”:””,”category_name”:”CVE”,”post_link”:””,”product”:”OpenSSL”,”version”:”3.6.0″,”vendor”:”OpenSSL”,”ai_description”:””,”ai_severity”:””,”ai_vendor”:””,”ai_product”:””,”ai_version”:””,”ai_score”:0}<\/p>\n","protected":false},"excerpt":{"rendered":"
{“lastseen”:””,”description”:”Issue summary: A TLS 1.3 connection using certificate compression can be\\nforced to allocate a large buffer before decompression without checking\\nagainst the configured certificate size limit.\\n\\nImpact…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2],"tags":[6,8,97,12,21,13,7,11,5],"class_list":["post-38130","post","type-post","status-publish","format-standard","hentry","category-category_cve","tag-cve","tag-cvss","tag-cvss-59","tag-exploit","tag-medium","tag-news","tag-security","tag-tapic","tag-vulnerability"],"yoast_head":"\n