GCVE Workshop - 22 September 2026 (14:00-18:00), Luxembourg Before The Vulnopticon Conference - Registration

CVE-2026-73251 (GCVE-0-2026-73251)

Vulnerability from cvelistv5 – Published: 2026-08-20 17:34 – Updated: 2026-08-20 19:50
VLAI
Title
Mongoose Built-in TLS: CA-bundle certificate chain accepted without any signature verification
Summary
Mongoose is an embedded web server and network library. Prior to 7.23, a network attacker can impersonate a TLS server to a Mongoose client configured with a multi-certificate CA bundle. In src/tls_builtin.c, the mg_tls_init() function stores the bundle in tls->ca_bundle_der while tls->ca_der.len remains zero, and mg_tls_recv_cert() uses tls_bundle_find() to accept a Common Name match without calling mg_tls_verify_cert_signature(). A forged self-signed certificate can therefore satisfy hostname and CertificateVerify checks and enable interception, credential disclosure, traffic modification, and malicious responses. This issue is fixed in version 7.23.
Severity
9.3 (Critical)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
SSVC
Exploitation: none Automatable: yes Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-08-20 19:50 UTC
CWE
  • CWE-295 - Improper Certificate Validation
Assigner
References
Impacted products
Vendor Product Version CPE status
cesanta mongoose Affected: < 7.23
guessed Create a notification for this product.
Show details on NVD website
To clipboard 

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-73251",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "total"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-08-20T19:50:25.364486Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-08-20T19:50:32.555Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "mongoose",
          "vendor": "cesanta",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 7.23"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "Mongoose is an embedded web server and network library. Prior to 7.23, a network attacker can impersonate a TLS server to a Mongoose client configured with a multi-certificate CA bundle. In src/tls_builtin.c, the mg_tls_init() function stores the bundle in tls-\u003eca_bundle_der while tls-\u003eca_der.len remains zero, and mg_tls_recv_cert() uses tls_bundle_find() to accept a Common Name match without calling mg_tls_verify_cert_signature(). A forged self-signed certificate can therefore satisfy hostname and CertificateVerify checks and enable interception, credential disclosure, traffic modification, and malicious responses. This issue is fixed in version 7.23."
        }
      ],
      "metrics": [
        {
          "cvssV4_0": {
            "attackComplexity": "LOW",
            "attackRequirements": "NONE",
            "attackVector": "NETWORK",
            "baseScore": 9.3,
            "baseSeverity": "CRITICAL",
            "privilegesRequired": "NONE",
            "subAvailabilityImpact": "NONE",
            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "NONE",
            "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N",
            "version": "4.0",
            "vulnAvailabilityImpact": "NONE",
            "vulnConfidentialityImpact": "HIGH",
            "vulnIntegrityImpact": "HIGH"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-295",
              "description": "CWE-295: Improper Certificate Validation",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-20T17:34:50.472Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/cesanta/mongoose/security/advisories/GHSA-qj6j-2692-v2r8",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/cesanta/mongoose/security/advisories/GHSA-qj6j-2692-v2r8"
        },
        {
          "name": "https://github.com/cesanta/mongoose/security/advisories/GHSA-qj6j-2692-v2r8",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/cesanta/mongoose/security/advisories/GHSA-qj6j-2692-v2r8"
        },
        {
          "name": "https://github.com/cesanta/mongoose/commit/2988bc9df3a5efc9539471cb7455975fa25df483",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/cesanta/mongoose/commit/2988bc9df3a5efc9539471cb7455975fa25df483"
        },
        {
          "name": "https://github.com/cesanta/mongoose/releases/tag/7.23",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/cesanta/mongoose/releases/tag/7.23"
        }
      ],
      "source": {
        "advisory": "GHSA-qj6j-2692-v2r8",
        "discovery": "UNKNOWN"
      },
      "title": "Mongoose Built-in TLS: CA-bundle certificate chain accepted without any signature verification"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-73251",
    "datePublished": "2026-08-20T17:34:50.472Z",
    "dateReserved": "2026-08-11T17:18:01.598Z",
    "dateUpdated": "2026-08-20T19:50:32.555Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-73251",
      "date": "2026-09-16",
      "epss": "0.00195",
      "percentile": "0.09504"
    },
    "nvd": "{\"cve\":{\"id\":\"CVE-2026-73251\",\"sourceIdentifier\":\"security-advisories@github.com\",\"published\":\"2026-08-20T18:16:45.743\",\"lastModified\":\"2026-09-09T21:19:49.197\",\"vulnStatus\":\"Awaiting Analysis\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"Mongoose is an embedded web server and network library. Prior to 7.23, a network attacker can impersonate a TLS server to a Mongoose client configured with a multi-certificate CA bundle. In src/tls_builtin.c, the mg_tls_init() function stores the bundle in tls-\u003eca_bundle_der while tls-\u003eca_der.len remains zero, and mg_tls_recv_cert() uses tls_bundle_find() to accept a Common Name match without calling mg_tls_verify_cert_signature(). A forged self-signed certificate can therefore satisfy hostname and CertificateVerify checks and enable interception, credential disclosure, traffic modification, and malicious responses. This issue is fixed in version 7.23.\"}],\"affected\":[{\"source\":\"security-advisories@github.com\",\"affectedData\":[{\"vendor\":\"cesanta\",\"product\":\"mongoose\",\"versions\":[{\"version\":\"\u003c 7.23\",\"status\":\"affected\"}]}]}],\"metrics\":{\"cvssMetricV40\":[{\"source\":\"security-advisories@github.com\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"4.0\",\"vectorString\":\"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X\",\"baseScore\":9.3,\"baseSeverity\":\"CRITICAL\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"LOW\",\"attackRequirements\":\"NONE\",\"privilegesRequired\":\"NONE\",\"userInteraction\":\"NONE\",\"vulnConfidentialityImpact\":\"HIGH\",\"vulnIntegrityImpact\":\"HIGH\",\"vulnAvailabilityImpact\":\"NONE\",\"subConfidentialityImpact\":\"NONE\",\"subIntegrityImpact\":\"NONE\",\"subAvailabilityImpact\":\"NONE\",\"exploitMaturity\":\"NOT_DEFINED\",\"confidentialityRequirement\":\"NOT_DEFINED\",\"integrityRequirement\":\"NOT_DEFINED\",\"availabilityRequirement\":\"NOT_DEFINED\",\"modifiedAttackVector\":\"NOT_DEFINED\",\"modifiedAttackComplexity\":\"NOT_DEFINED\",\"modifiedAttackRequirements\":\"NOT_DEFINED\",\"modifiedPrivilegesRequired\":\"NOT_DEFINED\",\"modifiedUserInteraction\":\"NOT_DEFINED\",\"modifiedVulnConfidentialityImpact\":\"NOT_DEFINED\",\"modifiedVulnIntegrityImpact\":\"NOT_DEFINED\",\"modifiedVulnAvailabilityImpact\":\"NOT_DEFINED\",\"modifiedSubConfidentialityImpact\":\"NOT_DEFINED\",\"modifiedSubIntegrityImpact\":\"NOT_DEFINED\",\"modifiedSubAvailabilityImpact\":\"NOT_DEFINED\",\"Safety\":\"NOT_DEFINED\",\"Automatable\":\"NOT_DEFINED\",\"Recovery\":\"NOT_DEFINED\",\"valueDensity\":\"NOT_DEFINED\",\"vulnerabilityResponseEffort\":\"NOT_DEFINED\",\"providerUrgency\":\"NOT_DEFINED\"}}],\"ssvcV203\":[{\"source\":\"134c704f-9b21-4f2e-91b3-4a467353bcc0\",\"ssvcData\":{\"timestamp\":\"2026-08-20T19:50:25.364486Z\",\"id\":\"CVE-2026-73251\",\"options\":[{\"exploitation\":\"none\"},{\"automatable\":\"yes\"},{\"technicalImpact\":\"total\"}],\"role\":\"CISA Coordinator\",\"version\":\"2.0.3\"}}]},\"weaknesses\":[{\"source\":\"security-advisories@github.com\",\"type\":\"Secondary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-295\"}]}],\"references\":[{\"url\":\"https://github.com/cesanta/mongoose/commit/2988bc9df3a5efc9539471cb7455975fa25df483\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/cesanta/mongoose/releases/tag/7.23\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/cesanta/mongoose/security/advisories/GHSA-qj6j-2692-v2r8\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/cesanta/mongoose/security/advisories/GHSA-qj6j-2692-v2r8\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/cesanta/mongoose/security/advisories/GHSA-qj6j-2692-v2r8\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/cesanta/mongoose/security/advisories/GHSA-qj6j-2692-v2r8\",\"source\":\"security-advisories@github.com\"}]}}",
    "vulnrichment": {
      "containers": "{\"adp\": [{\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2026-73251\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"none\"}, {\"Automatable\": \"yes\"}, {\"Technical Impact\": \"total\"}], \"version\": \"2.0.3\", \"timestamp\": \"2026-08-20T19:50:25.364486Z\"}}}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2026-08-20T19:50:28.634Z\"}}], \"cna\": {\"title\": \"Mongoose Built-in TLS: CA-bundle certificate chain accepted without any signature verification\", \"source\": {\"advisory\": \"GHSA-qj6j-2692-v2r8\", \"discovery\": \"UNKNOWN\"}, \"metrics\": [{\"cvssV4_0\": {\"version\": \"4.0\", \"baseScore\": 9.3, \"attackVector\": \"NETWORK\", \"baseSeverity\": \"CRITICAL\", \"vectorString\": \"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N\", \"userInteraction\": \"NONE\", \"attackComplexity\": \"LOW\", \"attackRequirements\": \"NONE\", \"privilegesRequired\": \"NONE\", \"subIntegrityImpact\": \"NONE\", \"vulnIntegrityImpact\": \"HIGH\", \"subAvailabilityImpact\": \"NONE\", \"vulnAvailabilityImpact\": \"NONE\", \"subConfidentialityImpact\": \"NONE\", \"vulnConfidentialityImpact\": \"HIGH\"}}], \"affected\": [{\"vendor\": \"cesanta\", \"product\": \"mongoose\", \"versions\": [{\"status\": \"affected\", \"version\": \"\u003c 7.23\"}]}], \"references\": [{\"url\": \"https://github.com/cesanta/mongoose/security/advisories/GHSA-qj6j-2692-v2r8\", \"name\": \"https://github.com/cesanta/mongoose/security/advisories/GHSA-qj6j-2692-v2r8\", \"tags\": [\"x_refsource_CONFIRM\"]}, {\"url\": \"https://github.com/cesanta/mongoose/security/advisories/GHSA-qj6j-2692-v2r8\", \"name\": \"https://github.com/cesanta/mongoose/security/advisories/GHSA-qj6j-2692-v2r8\", \"tags\": [\"x_refsource_MISC\"]}, {\"url\": \"https://github.com/cesanta/mongoose/commit/2988bc9df3a5efc9539471cb7455975fa25df483\", \"name\": \"https://github.com/cesanta/mongoose/commit/2988bc9df3a5efc9539471cb7455975fa25df483\", \"tags\": [\"x_refsource_MISC\"]}, {\"url\": \"https://github.com/cesanta/mongoose/releases/tag/7.23\", \"name\": \"https://github.com/cesanta/mongoose/releases/tag/7.23\", \"tags\": [\"x_refsource_MISC\"]}], \"descriptions\": [{\"lang\": \"en\", \"value\": \"Mongoose is an embedded web server and network library. Prior to 7.23, a network attacker can impersonate a TLS server to a Mongoose client configured with a multi-certificate CA bundle. In src/tls_builtin.c, the mg_tls_init() function stores the bundle in tls-\u003eca_bundle_der while tls-\u003eca_der.len remains zero, and mg_tls_recv_cert() uses tls_bundle_find() to accept a Common Name match without calling mg_tls_verify_cert_signature(). A forged self-signed certificate can therefore satisfy hostname and CertificateVerify checks and enable interception, credential disclosure, traffic modification, and malicious responses. This issue is fixed in version 7.23.\"}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-295\", \"description\": \"CWE-295: Improper Certificate Validation\"}]}], \"providerMetadata\": {\"orgId\": \"a0819718-46f1-4df5-94e2-005712e83aaa\", \"shortName\": \"GitHub_M\", \"dateUpdated\": \"2026-08-20T17:34:50.472Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-73251\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-08-20T19:50:32.555Z\", \"dateReserved\": \"2026-08-11T17:18:01.598Z\", \"assignerOrgId\": \"a0819718-46f1-4df5-94e2-005712e83aaa\", \"datePublished\": \"2026-08-20T17:34:50.472Z\", \"assignerShortName\": \"GitHub_M\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



Log in or create an account to share your comment.




Tags
Taxonomy of the tags.





Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.


Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.