CVE-2026-9545 (GCVE-0-2026-9545)
Vulnerability from cvelistv5 – Published: 2026-07-03 06:17 – Updated: 2026-07-03 06:17
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transfers, and when it makes a second transfer to the same site it has been
replaced by the attacker's impostor machine - without a valid certificate.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.
Severity ?
No CVSS data available.
Assigner
References
Impacted products
| Vendor | Product | Version | ||
|---|---|---|---|---|
| curl | curl |
Affected:
8.20.0 , ≤ 8.20.0
(semver)
Affected: 8.19.0 , ≤ 8.19.0 (semver) Affected: 8.18.0 , ≤ 8.18.0 (semver) Affected: 8.17.0 , ≤ 8.17.0 (semver) Affected: 8.16.0 , ≤ 8.16.0 (semver) Affected: 8.15.0 , ≤ 8.15.0 (semver) Affected: 8.14.1 , ≤ 8.14.1 (semver) Affected: 8.14.0 , ≤ 8.14.0 (semver) Affected: 8.13.0 , ≤ 8.13.0 (semver) Affected: 8.12.1 , ≤ 8.12.1 (semver) Affected: 8.12.0 , ≤ 8.12.0 (semver) Affected: 8.11.1 , ≤ 8.11.1 (semver) Affected: 8.11.0 , ≤ 8.11.0 (semver) |
Credits
Eunsoo Kim (Autonomous Code Security team at Microsoft)
Stefan Eissing
{
"containers": {
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{
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],
"credits": [
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"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": [
{
"description": "CWE-200 Exposure of Sensitive Information to an Unauthorized Actor",
"lang": "en"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-07-03T06:17:55.931Z",
"orgId": "2499f714-1537-4658-8207-48ae4bb9eae9",
"shortName": "curl"
},
"references": [
{
"name": "json",
"url": "https://curl.se/docs/CVE-2026-9545.json"
},
{
"name": "www",
"url": "https://curl.se/docs/CVE-2026-9545.html"
},
{
"name": "issue",
"url": "https://hackerone.com/reports/3752888"
}
],
"title": "exposing HTTP/3 early data"
}
},
"cveMetadata": {
"assignerOrgId": "2499f714-1537-4658-8207-48ae4bb9eae9",
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"cveId": "CVE-2026-9545",
"datePublished": "2026-07-03T06:17:55.931Z",
"dateReserved": "2026-05-26T06:45:08.680Z",
"dateUpdated": "2026-07-03T06:17:55.931Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
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Sightings
| Author | Source | Type | Date |
|---|
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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