CVE-2025-66199 (GCVE-0-2025-66199)

Vulnerability from cvelistv5 – Published: 2026-01-27 16:01 – Updated: 2026-01-29 15:03
VLAI
Title
TLS 1.3 CompressedCertificate excessive memory allocation
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.
Severity
5.9 (Medium)
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-01-29 15:03 UTC
CWE
  • CWE-789 - Memory Allocation with Excessive Size Value
Assigner
openssl CNA under the mitre root
CNA scorecard B 78/100 over 48 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
OpenSSL OpenSSL Affected: 3.6.0 , < 3.6.1 (semver)
Affected: 3.5.0 , < 3.5.5 (semver)
Affected: 3.4.0 , < 3.4.4 (semver)
Affected: 3.3.0 , < 3.3.6 (semver)
guessed Create a notification for this product.
Date Public
2026-01-27 14:00
Credits
Tomas Dulka (Aisle Research) Stanislav Fort (Aisle Research) Tomas Dulka (Aisle Research) Stanislav Fort (Aisle Research)
Show details on NVD website
To clipboard 

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            "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."
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            "value": "Resumen del problema: Una conexi\u00f3n TLS 1.3 que utiliza compresi\u00f3n de certificados puede ser forzada a asignar un b\u00fafer grande antes de la descompresi\u00f3n sin verificar contra el l\u00edmite de tama\u00f1o de certificado configurado.\n\nResumen del impacto: Un atacante puede causar asignaciones de memoria por conexi\u00f3n de hasta aproximadamente 22 MiB y trabajo adicional de CPU, lo que podr\u00eda llevar a degradaci\u00f3n del servicio o agotamiento de recursos (denegaci\u00f3n de servicio).\n\nEn configuraciones afectadas, la longitud del certificado sin comprimir proporcionada por el par de un mensaje CompressedCertificate se utiliza para aumentar un b\u00fafer de pila antes de la descompresi\u00f3n. Esta longitud no est\u00e1 limitada por la configuraci\u00f3n max_cert_list, que de otro modo restringe los tama\u00f1os de los mensajes de certificado. Un atacante puede explotar esto para causar grandes asignaciones por conexi\u00f3n seguidas de un fallo en el handshake. No ocurre corrupci\u00f3n de memoria ni revelaci\u00f3n de informaci\u00f3n.\n\nEste problema solo afecta a las compilaciones donde la compresi\u00f3n de certificados TLS 1.3 est\u00e1 compilada (es decir, no OPENSSL_NO_COMP_ALG) y al menos un algoritmo de compresi\u00f3n (brotli, zlib o zstd) est\u00e1 disponible, y donde la extensi\u00f3n de compresi\u00f3n es negociada. Tanto los clientes que reciben un CompressedCertificate del servidor como los servidores en escenarios TLS mutuos que reciben un CompressedCertificate del cliente se ven afectados. Los servidores que no solicitan certificados de cliente no son vulnerables a ataques iniciados por el cliente.\n\nLos usuarios pueden mitigar este problema configurando SSL_OP_NO_RX_CERTIFICATE_COMPRESSION para deshabilitar la recepci\u00f3n de certificados comprimidos.\n\nLos m\u00f3dulos FIPS en 3.6, 3.5, 3.4 y 3.3 no se ven afectados por este problema, ya que la implementaci\u00f3n de TLS est\u00e1 fuera del l\u00edmite del m\u00f3dulo FIPS de OpenSSL.\n\nOpenSSL 3.6, 3.5, 3.4 y 3.3 son vulnerables a este problema.\n\nOpenSSL 3.0, 1.1.1 y 1.0.2 no se ven afectados por este problema."
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              "dateUpdated": "2026-01-29T15:03:34.645Z",
              "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "shortName": "CISA-ADP"
            },
            "title": "CISA ADP Vulnrichment"
          }
        ],
        "cna": {
          "affected": [
            {
              "defaultStatus": "unaffected",
              "product": "OpenSSL",
              "vendor": "OpenSSL",
              "versions": [
                {
                  "lessThan": "3.6.1",
                  "status": "affected",
                  "version": "3.6.0",
                  "versionType": "semver"
                },
                {
                  "lessThan": "3.5.5",
                  "status": "affected",
                  "version": "3.5.0",
                  "versionType": "semver"
                },
                {
                  "lessThan": "3.4.4",
                  "status": "affected",
                  "version": "3.4.0",
                  "versionType": "semver"
                },
                {
                  "lessThan": "3.3.6",
                  "status": "affected",
                  "version": "3.3.0",
                  "versionType": "semver"
                }
              ]
            }
          ],
          "credits": [
            {
              "lang": "en",
              "type": "reporter",
              "value": "Tomas Dulka (Aisle Research)"
            },
            {
              "lang": "en",
              "type": "reporter",
              "value": "Stanislav Fort (Aisle Research)"
            },
            {
              "lang": "en",
              "type": "remediation developer",
              "value": "Tomas Dulka (Aisle Research)"
            },
            {
              "lang": "en",
              "type": "remediation developer",
              "value": "Stanislav Fort (Aisle Research)"
            }
          ],
          "datePublic": "2026-01-27T14:00:00.000Z",
          "descriptions": [
            {
              "lang": "en",
              "supportingMedia": [
                {
                  "base64": false,
                  "type": "text/html",
                  "value": "Issue summary: A TLS 1.3 connection using certificate compression can be\u003cbr\u003eforced to allocate a large buffer before decompression without checking\u003cbr\u003eagainst the configured certificate size limit.\u003cbr\u003e\u003cbr\u003eImpact summary: An attacker can cause per-connection memory allocations of\u003cbr\u003eup to approximately 22 MiB and extra CPU work, potentially leading to\u003cbr\u003eservice degradation or resource exhaustion (Denial of Service).\u003cbr\u003e\u003cbr\u003eIn affected configurations, the peer-supplied uncompressed certificate\u003cbr\u003elength from a CompressedCertificate message is used to grow a heap buffer\u003cbr\u003eprior to decompression. This length is not bounded by the max_cert_list\u003cbr\u003esetting, which otherwise constrains certificate message sizes. An attacker\u003cbr\u003ecan exploit this to cause large per-connection allocations followed by\u003cbr\u003ehandshake failure. No memory corruption or information disclosure occurs.\u003cbr\u003e\u003cbr\u003eThis issue only affects builds where TLS 1.3 certificate compression is\u003cbr\u003ecompiled in (i.e., not OPENSSL_NO_COMP_ALG) and at least one compression\u003cbr\u003ealgorithm (brotli, zlib, or zstd) is available, and where the compression\u003cbr\u003eextension is negotiated. Both clients receiving a server CompressedCertificate\u003cbr\u003eand servers in mutual TLS scenarios receiving a client CompressedCertificate\u003cbr\u003eare affected. Servers that do not request client certificates are not\u003cbr\u003evulnerable to client-initiated attacks.\u003cbr\u003e\u003cbr\u003eUsers can mitigate this issue by setting SSL_OP_NO_RX_CERTIFICATE_COMPRESSION\u003cbr\u003eto disable receiving compressed certificates.\u003cbr\u003e\u003cbr\u003eThe FIPS modules in 3.6, 3.5, 3.4 and 3.3 are not affected by this issue,\u003cbr\u003eas the TLS implementation is outside the OpenSSL FIPS module boundary.\u003cbr\u003e\u003cbr\u003eOpenSSL 3.6, 3.5, 3.4 and 3.3 are vulnerable to this issue.\u003cbr\u003e\u003cbr\u003eOpenSSL 3.0, 1.1.1 and 1.0.2 are not affected by this issue."
                }
              ],
              "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."
            }
          ],
          "metrics": [
            {
              "format": "other",
              "other": {
                "content": {
                  "text": "Low"
                },
                "type": "https://openssl-library.org/policies/general/security-policy/"
              }
            }
          ],
          "problemTypes": [
            {
              "descriptions": [
                {
                  "cweId": "CWE-789",
                  "description": "CWE-789 Memory Allocation with Excessive Size Value",
                  "lang": "en",
                  "type": "CWE"
                }
              ]
            }
          ],
          "providerMetadata": {
            "dateUpdated": "2026-01-27T16:01:22.399Z",
            "orgId": "3a12439a-ef3a-4c79-92e6-6081a721f1e5",
            "shortName": "openssl"
          },
          "references": [
            {
              "name": "OpenSSL Advisory",
              "tags": [
                "vendor-advisory"
              ],
              "url": "https://openssl-library.org/news/secadv/20260127.txt"
            },
            {
              "name": "3.6.1 git commit",
              "tags": [
                "patch"
              ],
              "url": "https://github.com/openssl/openssl/commit/6184a4fb08ee6d7bca570d931a4e8bef40b64451"
            },
            {
              "name": "3.5.5 git commit",
              "tags": [
                "patch"
              ],
              "url": "https://github.com/openssl/openssl/commit/895150b5e021d16b52fb32b97e1dd12f20448be5"
            },
            {
              "name": "3.4.4 git commit",
              "tags": [
                "patch"
              ],
              "url": "https://github.com/openssl/openssl/commit/966a2478046c311ed7dae50c457d0db4cafbf7e4"
            },
            {
              "name": "3.3.6 git commit",
              "tags": [
                "patch"
              ],
              "url": "https://github.com/openssl/openssl/commit/3ed1f75249932b155eef993a8e66a99cb98bfef4"
            }
          ],
          "source": {
            "discovery": "UNKNOWN"
          },
          "title": "TLS 1.3 CompressedCertificate excessive memory allocation",
          "x_generator": {
            "engine": "Vulnogram 0.2.0"
          }
        }
      },
      "cveMetadata": {
        "assignerOrgId": "3a12439a-ef3a-4c79-92e6-6081a721f1e5",
        "assignerShortName": "openssl",
        "cveId": "CVE-2025-66199",
        "datePublished": "2026-01-27T16:01:22.399Z",
        "dateReserved": "2025-11-24T15:00:43.637Z",
        "dateUpdated": "2026-01-29T15:03:51.754Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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Sightings

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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
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  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
Vulnerability timeline

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