CVE-2026-9545 (GCVE-0-2026-9545)

Vulnerability from cvelistv5 – Published: 2026-07-03 06:17 – Updated: 2026-09-15 06:03
VLAI
Title
exposing HTTP/3 early data
Summary
In this scenario, libcurl first uses a proper HTTP/3 server for the initial transfers, and when it makes a second transfer to the same site it has been replaced by the attacker's impostor machine - without a valid certificate. When libcurl returns to the hostname the second time with a cached SSL session (`CURLOPT_SSL_SESSIONID_CACHE` is not disabled) and early data enabled (the `CURLSSLOPT_EARLYDATA` bit is set in `CURLOPT_SSL_OPTIONS`), libcurl might send off the second request's bytes on that new connection *before* enforcing the certificate verification failure. Potentially leaking sensitive information.
SSVC
Exploitation: poc Automatable: yes Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-07-06 16:52 UTC
CWE
  • CWE-200 - Exposure of Sensitive Information to an Unauthorized Actor
Impacted products
Vendor Product Version CPE status
curl curl Affected: 8.11.0 , < 8.14.2 (semver)
Affected: 8.15.0 , < 8.16.1 (semver)
Affected: 8.17.0 , < 8.20.1 (semver)
guessed Create a notification for this product.
curl curl Affected: 962097b8dd44ed5b9e7984bc1cdffdbdd566857f , < 7b9613fa9b1a5e04301a3920eef58e8138dad05e (git)
guessed Create a notification for this product.
curl curl Affected: 8.20.0
Affected: 8.19.0
Affected: 8.18.0
Affected: 8.17.0
Affected: 8.16.0
Affected: 8.15.0
Affected: 8.14.1
Affected: 8.14.0
Affected: 8.13.0
Affected: 8.12.1
Affected: 8.12.0
Affected: 8.11.1
Affected: 8.11.0
guessed Create a notification for this product.
Show details on NVD website

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                  "version": "8.19.0"
                },
                {
                  "status": "affected",
                  "version": "8.18.0"
                },
                {
                  "status": "affected",
                  "version": "8.17.0"
                },
                {
                  "status": "affected",
                  "version": "8.16.0"
                },
                {
                  "status": "affected",
                  "version": "8.15.0"
                },
                {
                  "status": "affected",
                  "version": "8.14.1"
                },
                {
                  "status": "affected",
                  "version": "8.14.0"
                },
                {
                  "status": "affected",
                  "version": "8.13.0"
                },
                {
                  "status": "affected",
                  "version": "8.12.1"
                },
                {
                  "status": "affected",
                  "version": "8.12.0"
                },
                {
                  "status": "affected",
                  "version": "8.11.1"
                },
                {
                  "status": "affected",
                  "version": "8.11.0"
                }
              ]
            }
          ],
          "credits": [
            {
              "lang": "en",
              "type": "finder",
              "value": "Eunsoo Kim (Autonomous Code Security team at Microsoft)"
            },
            {
              "lang": "en",
              "type": "remediation developer",
              "value": "Stefan Eissing"
            }
          ],
          "descriptions": [
            {
              "lang": "en",
              "value": "In this scenario, libcurl first uses a proper HTTP/3 server for the initial\ntransfers, and when it makes a second transfer to the same site it has been\nreplaced by the attacker\u0027s impostor machine - without a valid certificate.\n\nWhen libcurl returns to the hostname the second time with a cached SSL session\n(`CURLOPT_SSL_SESSIONID_CACHE` is not disabled) and early data enabled (the\n`CURLSSLOPT_EARLYDATA` bit is set in `CURLOPT_SSL_OPTIONS`), libcurl might\nsend off the second request\u0027s bytes on that new connection *before* enforcing\nthe certificate verification failure. Potentially leaking sensitive\ninformation."
            }
          ],
          "problemTypes": [
            {
              "descriptions": [
                {
                  "cweId": "CWE-200",
                  "description": "Exposure of Sensitive Information to an Unauthorized Actor",
                  "lang": "en",
                  "type": "CWE"
                }
              ]
            }
          ],
          "providerMetadata": {
            "dateUpdated": "2026-09-15T06:03:31.804Z",
            "orgId": "2499f714-1537-4658-8207-48ae4bb9eae9",
            "shortName": "curl"
          },
          "references": [
            {
              "url": "https://curl.se/docs/CVE-2026-9545.json"
            },
            {
              "url": "https://curl.se/docs/CVE-2026-9545.html"
            },
            {
              "url": "https://hackerone.com/reports/3752888"
            }
          ],
          "title": "exposing HTTP/3 early data",
          "x_generator": {
            "engine": "cvelib 1.8.0"
          },
          "x_osv": {
            "affected": [
              {
                "ranges": [
                  {
                    "events": [
                      {
                        "introduced": "8.11.0"
                      },
                      {
                        "fixed": "8.14.2"
                      },
                      {
                        "introduced": "8.15.0"
                      },
                      {
                        "fixed": "8.16.1"
                      },
                      {
                        "introduced": "8.17.0"
                      },
                      {
                        "fixed": "8.20.1"
                      }
                    ],
                    "type": "SEMVER"
                  },
                  {
                    "events": [
                      {
                        "introduced": "962097b8dd44ed5b9e7984bc1cdffdbdd566857f"
                      },
                      {
                        "fixed": "7b9613fa9b1a5e04301a3920eef58e8138dad05e"
                      }
                    ],
                    "repo": "https://github.com/curl/curl.git",
                    "type": "GIT"
                  }
                ],
                "versions": [
                  "8.20.0",
                  "8.19.0",
                  "8.18.0",
                  "8.17.0",
                  "8.16.0",
                  "8.15.0",
                  "8.14.1",
                  "8.14.0",
                  "8.13.0",
                  "8.12.1",
                  "8.12.0",
                  "8.11.1",
                  "8.11.0"
                ]
              }
            ],
            "aliases": [
              "CVE-2026-9545"
            ],
            "credits": [
              {
                "name": "Eunsoo Kim (Autonomous Code Security team at Microsoft)",
                "type": "finder"
              },
              {
                "name": "Stefan Eissing",
                "type": "remediation developer"
              }
            ],
            "database_specific": {
              "CWE": {
                "desc": "Exposure of Sensitive Information to an Unauthorized Actor",
                "id": "CWE-200"
              },
              "URL": "https://curl.se/docs/CVE-2026-9545.json",
              "affects": "both",
              "issue": "https://hackerone.com/reports/3752888",
              "last_affected": "8.20.0",
              "package": "curl",
              "severity": "Low",
              "www": "https://curl.se/docs/CVE-2026-9545.html"
            },
            "details": "In this scenario, libcurl first uses a proper HTTP/3 server for the initial\ntransfers, and when it makes a second transfer to the same site it has been\nreplaced by the attacker\u0027s impostor machine - without a valid certificate.\n\nWhen libcurl returns to the hostname the second time with a cached SSL session\n(`CURLOPT_SSL_SESSIONID_CACHE` is not disabled) and early data enabled (the\n`CURLSSLOPT_EARLYDATA` bit is set in `CURLOPT_SSL_OPTIONS`), libcurl might\nsend off the second request\u0027s bytes on that new connection *before* enforcing\nthe certificate verification failure. Potentially leaking sensitive\ninformation.",
            "id": "CURL-CVE-2026-9545",
            "modified": "2026-09-07T10:34:51.00Z",
            "published": "2026-06-24T08:00:00.00Z",
            "schema_version": "1.5.0",
            "summary": "exposing HTTP/3 early data"
          }
        }
      },
      "cveMetadata": {
        "assignerOrgId": "2499f714-1537-4658-8207-48ae4bb9eae9",
        "assignerShortName": "curl",
        "cveId": "CVE-2026-9545",
        "datePublished": "2026-07-03T06:17:55.931Z",
        "dateReserved": "2026-05-26T06:45:08.680Z",
        "dateUpdated": "2026-09-15T06:03:31.804Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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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.

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Detection rules are retrieved from Rulezet.

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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.


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