CVE-2026-72897 (GCVE-0-2026-72897)

Vulnerability from cvelistv5 – Published: 2026-09-29 15:32 – Updated: 2026-09-29 17:16
VLAI
Title
Out-of-Bounds Access After SSL_set_SSL_CTX() During a Handshake
Summary
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 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.
Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
SSVC
Exploitation: none Automatable: yes Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-09-29 17:16 UTC
CWE
Assigner
openssl CNA under the mitre root
CNA scorecard B 78/100 over 43 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
OpenSSL OpenSSL Affected: 4.0.0 , < 4.0.3 (semver)
Affected: 3.6.0 , < 3.6.5 (semver)
Affected: 3.5.0 , < 3.5.9 (semver)
Affected: 3.4.0 , < 3.4.8 (semver)
guessed Create a notification for this product.
Date Public
2026-09-29 14:21
Credits
Filipe Casal (Trail of Bits) Brandon Luo Luigino Camastra (Aisle Research) Matt Caswell
Show details on NVD website
To clipboard 

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      "status": "interim",
      "title": "SUSE CVE CVE-2026-72897",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/2026/cve-2026-72897.json",
      "version": "6"
    },
    "vulnrichment": {
      "containers": {
        "adp": [
          {
            "metrics": [
              {
                "cvssV3_1": {
                  "attackComplexity": "LOW",
                  "attackVector": "NETWORK",
                  "availabilityImpact": "HIGH",
                  "baseScore": 7.5,
                  "baseSeverity": "HIGH",
                  "confidentialityImpact": "NONE",
                  "integrityImpact": "NONE",
                  "privilegesRequired": "NONE",
                  "scope": "UNCHANGED",
                  "userInteraction": "NONE",
                  "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
                  "version": "3.1"
                }
              },
              {
                "other": {
                  "content": {
                    "id": "CVE-2026-72897",
                    "options": [
                      {
                        "Exploitation": "none"
                      },
                      {
                        "Automatable": "yes"
                      },
                      {
                        "Technical Impact": "partial"
                      }
                    ],
                    "role": "CISA Coordinator",
                    "timestamp": "2026-09-29T17:16:29.979390Z",
                    "version": "2.0.3"
                  },
                  "type": "ssvc"
                }
              }
            ],
            "providerMetadata": {
              "dateUpdated": "2026-09-29T17:16:22.301Z",
              "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "shortName": "CISA-ADP"
            },
            "title": "CISA ADP Vulnrichment"
          }
        ],
        "cna": {
          "affected": [
            {
              "defaultStatus": "unaffected",
              "product": "OpenSSL",
              "vendor": "OpenSSL",
              "versions": [
                {
                  "lessThan": "4.0.3",
                  "status": "affected",
                  "version": "4.0.0",
                  "versionType": "semver"
                },
                {
                  "lessThan": "3.6.5",
                  "status": "affected",
                  "version": "3.6.0",
                  "versionType": "semver"
                },
                {
                  "lessThan": "3.5.9",
                  "status": "affected",
                  "version": "3.5.0",
                  "versionType": "semver"
                },
                {
                  "lessThan": "3.4.8",
                  "status": "affected",
                  "version": "3.4.0",
                  "versionType": "semver"
                }
              ]
            }
          ],
          "credits": [
            {
              "lang": "en",
              "type": "reporter",
              "value": "Filipe Casal (Trail of Bits)"
            },
            {
              "lang": "en",
              "type": "reporter",
              "value": "Brandon Luo"
            },
            {
              "lang": "en",
              "type": "reporter",
              "value": "Luigino Camastra (Aisle Research)"
            },
            {
              "lang": "en",
              "type": "remediation developer",
              "value": "Matt Caswell"
            }
          ],
          "datePublic": "2026-09-29T14:21:57.000Z",
          "descriptions": [
            {
              "lang": "en",
              "supportingMedia": [
                {
                  "base64": false,
                  "type": "text/html",
                  "value": "Issue summary: A TLS server that calls SSL_set_SSL_CTX() to switch a\u003cbr\u003econnection to a different SSL_CTX part way through a handshake may access\u003cbr\u003ememory beyond the end of an internal array if the replacement context knows\u003cbr\u003eabout more provider signature algorithms than the context the connection was\u003cbr\u003ecreated from. Applications which never call SSL_set_SSL_CTX() are not\u003cbr\u003eaffected.\u003cbr\u003e\u003cbr\u003eImpact summary: A remote peer may be able to cause a small out-of-bounds\u003cbr\u003eread, and in some circumstances a fixed-value out-of-bounds write, on the\u003cbr\u003eserver heap. This may lead to a Denial of Service.\u003cbr\u003e\u003cbr\u003eCWE: CWE-787: Out-of-bounds Write\u003cbr\u003e\u003cbr\u003eDescription: A TLS connection records how many certificate slots it has\u003cbr\u003ewhen it is created, taken from the SSL_CTX that created it: the built-in\u003cbr\u003ecertificate types plus one slot for each provider TLS-SIGALG entry that\u003cbr\u003econtext was aware of. That count sizes an internal array of per-slot\u003cbr\u003ecertificate validity flags.\u003cbr\u003e\u003cbr\u003eAn application may replace a connection\u0027s SSL_CTX part way through the\u003cbr\u003ehandshake by calling SSL_set_SSL_CTX(), most commonly from a servername\u003cbr\u003ecallback in order to serve a different virtual host. Doing so did not\u003cbr\u003erefresh the recorded count. A provider signature algorithm\u0027s slot index is\u003cbr\u003eits position in the list of whichever context resolves it, so if the\u003cbr\u003ereplacement context is aware of more of them than the original, an\u003cbr\u003ealgorithm offered by the peer can resolve to an index beyond the end of the\u003cbr\u003earray. Processing the peer\u0027s signature algorithms then reads one four byte\u003cbr\u003eword past the end for each such algorithm and, where the word read is zero,\u003cbr\u003ewrites a fixed value over it. A peer offering many of them can corrupt heap\u003cbr\u003emetadata and abort the process.\u003cbr\u003e\u003cbr\u003eOnly provider signature algorithms which occupy one of the excess slots,\u003cbr\u003eand which the server also has configured, have this effect. Codepoints the\u003cbr\u003ereplacement context does not recognise are discarded without being resolved\u003cbr\u003eto a slot, and provider signature algorithms are usable only from TLS 1.3.\u003cbr\u003e\u003cbr\u003eThe two contexts must therefore be aware of different numbers of provider\u003cbr\u003esignature algorithms, which requires separate library contexts, a provider\u003cbr\u003eloaded between the two being created, or providers which differ in what\u003cbr\u003ethey advertise - in 4.0, for example, the default provider advertises SM2\u003cbr\u003ewhere the FIPS provider does not. A deployment meeting the condition is\u003cbr\u003ealso unable to negotiate the affected algorithms with legitimate clients,\u003cbr\u003esince the same stale count hides the corresponding certificates, so the\u003cbr\u003emisconfiguration is likely to be noticed. For that reason, and because the\u003cbr\u003econfiguration is not the default, this issue has been assessed as Low\u003cbr\u003eseverity.\u003cbr\u003e\u003cbr\u003eFIPS impact: no\u003cbr\u003eNo FIPS modules are affected by this issue as the affected code is outside\u003cbr\u003ethe OpenSSL FIPS module boundary."
                }
              ],
              "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\u0027s 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\u0027s 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\u0027s 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."
            }
          ],
          "metrics": [
            {
              "format": "other",
              "other": {
                "content": {
                  "text": "Low"
                },
                "type": "https://openssl-library.org/policies/general/security-policy/"
              }
            }
          ],
          "problemTypes": [
            {
              "descriptions": [
                {
                  "cweId": "CWE-787",
                  "description": "CWE-787 Out-of-bounds Write",
                  "lang": "en",
                  "type": "CWE"
                }
              ]
            }
          ],
          "providerMetadata": {
            "dateUpdated": "2026-09-29T15:32:18.277Z",
            "orgId": "3a12439a-ef3a-4c79-92e6-6081a721f1e5",
            "shortName": "openssl"
          },
          "references": [
            {
              "name": "OpenSSL Advisory",
              "tags": [
                "vendor-advisory"
              ],
              "url": "https://openssl-library.org/news/secadv/20260929.txt"
            },
            {
              "name": "4.0.3 git commit",
              "tags": [
                "patch"
              ],
              "url": "https://github.com/openssl/openssl/commit/e87ed26b298a74d8ba61a53e9c7bcd1acac6b814"
            },
            {
              "name": "3.6.5 git commit",
              "tags": [
                "patch"
              ],
              "url": "https://github.com/openssl/openssl/commit/9c54d209486f6b1ad79fe2179c40f13200fa4f61"
            },
            {
              "name": "3.5.9 git commit",
              "tags": [
                "patch"
              ],
              "url": "https://github.com/openssl/openssl/commit/4135f553c9d3ba4a09fe752f5d30af2a6a092b2e"
            },
            {
              "name": "3.4.8 git commit",
              "tags": [
                "patch"
              ],
              "url": "https://github.com/openssl/openssl/commit/00646e5085a0d12d29e0d2f9b9bc5f7111a50922"
            }
          ],
          "source": {
            "discovery": "UNKNOWN"
          },
          "title": "Out-of-Bounds Access After SSL_set_SSL_CTX() During a Handshake",
          "x_generator": {
            "engine": "Vulnogram 0.2.0"
          }
        }
      },
      "cveMetadata": {
        "assignerOrgId": "3a12439a-ef3a-4c79-92e6-6081a721f1e5",
        "assignerShortName": "openssl",
        "cveId": "CVE-2026-72897",
        "datePublished": "2026-09-29T15:32:18.277Z",
        "dateReserved": "2026-08-10T17:02:46.613Z",
        "dateUpdated": "2026-09-29T17:16:38.842Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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