FKIE_CVE-2025-66199

Vulnerability from fkie_nvd - Published: 2026-01-27 16:16 - Updated: 2026-01-29 16:31
Severity ?
5.9 (Medium) - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Summary
Issue summary: A TLS 1.3 connection using certificate compression can be forced to allocate a large buffer before decompression without checking against the configured certificate size limit. Impact summary: An attacker can cause per-connection memory allocations of up to approximately 22 MiB and extra CPU work, potentially leading to service degradation or resource exhaustion (Denial of Service). In affected configurations, the peer-supplied uncompressed certificate length from a CompressedCertificate message is used to grow a heap buffer prior to decompression. This length is not bounded by the max_cert_list setting, which otherwise constrains certificate message sizes. An attacker can exploit this to cause large per-connection allocations followed by handshake failure. No memory corruption or information disclosure occurs. This issue only affects builds where TLS 1.3 certificate compression is compiled in (i.e., not OPENSSL_NO_COMP_ALG) and at least one compression algorithm (brotli, zlib, or zstd) is available, and where the compression extension is negotiated. Both clients receiving a server CompressedCertificate and servers in mutual TLS scenarios receiving a client CompressedCertificate are affected. Servers that do not request client certificates are not vulnerable to client-initiated attacks. Users can mitigate this issue by setting SSL_OP_NO_RX_CERTIFICATE_COMPRESSION to disable receiving compressed certificates. The FIPS modules in 3.6, 3.5, 3.4 and 3.3 are not affected by this issue, as the TLS implementation is outside the OpenSSL FIPS module boundary. OpenSSL 3.6, 3.5, 3.4 and 3.3 are vulnerable to this issue. OpenSSL 3.0, 1.1.1 and 1.0.2 are not affected by this issue.
References
openssl-security@openssl.orghttps://github.com/openssl/openssl/commit/3ed1f75249932b155eef993a8e66a99cb98bfef4
openssl-security@openssl.orghttps://github.com/openssl/openssl/commit/6184a4fb08ee6d7bca570d931a4e8bef40b64451
openssl-security@openssl.orghttps://github.com/openssl/openssl/commit/895150b5e021d16b52fb32b97e1dd12f20448be5
openssl-security@openssl.orghttps://github.com/openssl/openssl/commit/966a2478046c311ed7dae50c457d0db4cafbf7e4
openssl-security@openssl.orghttps://openssl-library.org/news/secadv/20260127.txt
Impacted products
Vendor Product Version
To clipboard 

{
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "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."
    }
  ],
  "id": "CVE-2025-66199",
  "lastModified": "2026-01-29T16:31:35.700",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "HIGH",
          "attackVector": "NETWORK",
          "availabilityImpact": "HIGH",
          "baseScore": 5.9,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 2.2,
        "impactScore": 3.6,
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-01-27T16:16:15.777",
  "references": [
    {
      "source": "openssl-security@openssl.org",
      "url": "https://github.com/openssl/openssl/commit/3ed1f75249932b155eef993a8e66a99cb98bfef4"
    },
    {
      "source": "openssl-security@openssl.org",
      "url": "https://github.com/openssl/openssl/commit/6184a4fb08ee6d7bca570d931a4e8bef40b64451"
    },
    {
      "source": "openssl-security@openssl.org",
      "url": "https://github.com/openssl/openssl/commit/895150b5e021d16b52fb32b97e1dd12f20448be5"
    },
    {
      "source": "openssl-security@openssl.org",
      "url": "https://github.com/openssl/openssl/commit/966a2478046c311ed7dae50c457d0db4cafbf7e4"
    },
    {
      "source": "openssl-security@openssl.org",
      "url": "https://openssl-library.org/news/secadv/20260127.txt"
    }
  ],
  "sourceIdentifier": "openssl-security@openssl.org",
  "vulnStatus": "Awaiting Analysis",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-789"
        }
      ],
      "source": "openssl-security@openssl.org",
      "type": "Secondary"
    }
  ]
}


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