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CVE-2026-72897

Estado: En análisisAlta (7.5)—

Issue summary: A TLS server that calls SSL_set_SSL_CTX() to switch a connection to a different SSL_CTX part way through a handshake may access memory beyond the end of an internal array if the replacement context knows about more provider signature algorithms than the context the connection was created from. Applications which never call SSL_set_SSL_CTX() are not affected.

Impact summary: A remote peer may be able to cause a small out-of-bounds read, and in some circumstances a fixed-value out-of-bounds write, on the server heap. This may lead to a Denial of Service.

CWE: CWE-787: Out-of-bounds Write

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Description: A TLS connection records how many certificate slots it has when it is created, taken from the SSL_CTX that created it: the built-in certificate types plus one slot for each provider TLS-SIGALG entry that context was aware of. That count sizes an internal array of per-slot certificate validity flags.

An application may replace a connection's SSL_CTX part way through the handshake by calling SSL_set_SSL_CTX(), most commonly from a servername callback in order to serve a different virtual host. Doing so did not refresh the recorded count. A provider signature algorithm's slot index is its position in the list of whichever context resolves it, so if the replacement context is aware of more of them than the original, an algorithm offered by the peer can resolve to an index beyond the end of the array. Processing the peer's signature algorithms then reads one four byte word past the end for each such algorithm and, where the word read is zero, writes a fixed value over it. A peer offering many of them can corrupt heap metadata and abort the process.

Only provider signature algorithms which occupy one of the excess slots, and which the server also has configured, have this effect. Codepoints the replacement context does not recognise are discarded without being resolved to a slot, and provider signature algorithms are usable only from TLS 1.3.

The two contexts must therefore be aware of different numbers of provider signature algorithms, which requires separate library contexts, a provider loaded between the two being created, or providers which differ in what they advertise - in 4.0, for example, the default provider advertises SM2 where the FIPS provider does not. A deployment meeting the condition is also unable to negotiate the affected algorithms with legitimate clients, since the same stale count hides the corresponding certificates, so the misconfiguration is likely to be noticed. For that reason, and because the configuration is not the default, this issue has been assessed as Low severity.

FIPS impact: no No FIPS modules are affected by this issue as the affected code is outside the OpenSSL FIPS module boundary.

CVSS

Probabilidad de explotación (EPSS)

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

🎯 Técnicas ATT&CK

Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.

Vulnerabilidad en servidor TLS (OpenSSL) remotamente explotable sin autenticación. Lectura/escritura fuera de límites en heap causa DoS por corrupción de metadatos y terminación de proceso. CWE-787 corrobora.

Inferido por nuestro agente de análisis a partir de la descripción oficial, el vector CVSS y la CWE, y comprobado por un supervisor. Puede contener errores.

🛡️ Mitigaciones ATT&CK que cubren estas técnicas

Filter Network TrafficVulnerability ScanningPrivileged Account ManagementNetwork SegmentationLimit Access to Resource Over NetworkApplication Isolation and Sandboxing

Tecnologías afectadas (1)

⚠ Inferidas por IA a partir de la descripción — NVD aún no ha analizado esta CVE; no son CPE verificados.

Openssl — OpensslAI

CWE

Referencias

JSON original (NVD)

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{
  "id": "CVE-2026-72897",
  "cveTags": [],
  "metrics": {
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-72897",
          "role": "CISA Coordinator",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "yes"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "version": "2.0.3",
          "timestamp": "2026-09-29T17:16:29.979390Z"
        }
      }
    ],
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 7.5,
          "attackVector": "NETWORK",
          "baseSeverity": "HIGH",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
          "integrityImpact": "NONE",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "NONE"
        },
        "impactScore": 3.6,
        "exploitabilityScore": 3.9
      }
    ]
  },
  "affected": [
    {
      "source": "openssl-security@openssl.org",
      "affectedData": [
        {
          "vendor": "OpenSSL",
          "product": "OpenSSL",
          "versions": [
            {
              "status": "affected",
              "version": "4.0.0",
              "lessThan": "4.0.3",
              "versionType": "semver"
            },
            {
              "status": "affected",
              "version": "3.6.0",
              "lessThan": "3.6.5",
              "versionType": "semver"
            },
            {
              "status": "affected",
              "version": "3.5.0",
              "lessThan": "3.5.9",
              "versionType": "semver"
            },
            {
              "status": "affected",
              "version": "3.4.0",
              "lessThan": "3.4.8",
              "versionType": "semver"
            }
          ],
          "defaultStatus": "unaffected"
        }
      ]
    }
  ],
  "published": "2026-09-29T16:17:09.903",
  "references": [
    {
      "url": "https://github.com/openssl/openssl/commit/00646e5085a0d12d29e0d2f9b9bc5f7111a50922",
      "source": "openssl-security@openssl.org"
    },
    {
      "url": "https://github.com/openssl/openssl/commit/4135f553c9d3ba4a09fe752f5d30af2a6a092b2e",
      "source": "openssl-security@openssl.org"
    },
    {
      "url": "https://github.com/openssl/openssl/commit/9c54d209486f6b1ad79fe2179c40f13200fa4f61",
      "source": "openssl-security@openssl.org"
    },
    {
      "url": "https://github.com/openssl/openssl/commit/e87ed26b298a74d8ba61a53e9c7bcd1acac6b814",
      "source": "openssl-security@openssl.org"
    },
    {
      "url": "https://openssl-library.org/news/secadv/20260929.txt",
      "source": "openssl-security@openssl.org"
    }
  ],
  "vulnStatus": "Undergoing Analysis",
  "weaknesses": [
    {
      "type": "Secondary",
      "source": "openssl-security@openssl.org",
      "description": [
        {
          "lang": "en",
          "value": "CWE-787"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "Issue summary: A TLS server that calls SSL_set_SSL_CTX() to switch a\nconnection to a different SSL_CTX part way through a handshake may access\nmemory beyond the end of an internal array if the replacement context knows\nabout more provider signature algorithms than the context the connection was\ncreated from. Applications which never call SSL_set_SSL_CTX() are not\naffected.\n\nImpact summary: A remote peer may be able to cause a small out-of-bounds\nread, and in some circumstances a fixed-value out-of-bounds write, on the\nserver heap. This may lead to a Denial of Service.\n\nCWE: CWE-787: Out-of-bounds Write\n\nDescription: A TLS connection records how many certificate slots it has\nwhen it is created, taken from the SSL_CTX that created it: the built-in\ncertificate types plus one slot for each provider TLS-SIGALG entry that\ncontext was aware of. That count sizes an internal array of per-slot\ncertificate validity flags.\n\nAn application may replace a connection's SSL_CTX part way through the\nhandshake by calling SSL_set_SSL_CTX(), most commonly from a servername\ncallback in order to serve a different virtual host. Doing so did not\nrefresh the recorded count. A provider signature algorithm's slot index is\nits position in the list of whichever context resolves it, so if the\nreplacement context is aware of more of them than the original, an\nalgorithm offered by the peer can resolve to an index beyond the end of the\narray. Processing the peer's signature algorithms then reads one four byte\nword past the end for each such algorithm and, where the word read is zero,\nwrites a fixed value over it. A peer offering many of them can corrupt heap\nmetadata and abort the process.\n\nOnly provider signature algorithms which occupy one of the excess slots,\nand which the server also has configured, have this effect. Codepoints the\nreplacement context does not recognise are discarded without being resolved\nto a slot, and provider signature algorithms are usable only from TLS 1.3.\n\nThe two contexts must therefore be aware of different numbers of provider\nsignature algorithms, which requires separate library contexts, a provider\nloaded between the two being created, or providers which differ in what\nthey advertise - in 4.0, for example, the default provider advertises SM2\nwhere the FIPS provider does not. A deployment meeting the condition is\nalso unable to negotiate the affected algorithms with legitimate clients,\nsince the same stale count hides the corresponding certificates, so the\nmisconfiguration is likely to be noticed. For that reason, and because the\nconfiguration is not the default, this issue has been assessed as Low\nseverity.\n\nFIPS impact: no\nNo FIPS modules are affected by this issue as the affected code is outside\nthe OpenSSL FIPS module boundary."
    }
  ],
  "lastModified": "2026-09-29T21:27:41.130",
  "sourceIdentifier": "openssl-security@openssl.org"
}