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CVE-2026-9545

exposing HTTP/3 early data

Published: Jul 3, 2026Updated: Jul 7, 2026 Sources: CVE List NVDNVD-CWE-noinfo
7.5HIGH
NVD MITRE
EPSS Score
0.3%
Top 81.2%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available
Self-Check
OpenVAS

Description

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uses a proper HTTP/3 server for the initial transfers, and when it makes a second transfer to the same site it has been replaced by the attacker's impostor machine - without a valid certificate.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.

No summary for this CVE yet.

CVSS Vector Breakdown

AV:NAC:LPR:NUI:NS:UC:HI:NA:N
Exploitability
AV:NAttack Vector
Network
AC:LAttack Complexity
Low
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:HConfidentiality
High
I:NIntegrity
None
A:NAvailability
None
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Weaknesses

NVD-CWE-noinfo

Affected Products

haxx
oss-project·SEaka haxx.se
curl
OSS Libraries
curl
oss-project·USaka wcurl, libcurl
curlLibraryLibrary
OSS Libraries / generic-library

Exploitability

Official Patch Available
Is your org exposed to CVE-2026-9545?We can run the check for you — a free external exposure review, no install. Check my exposure

References

https://curl.se/docs/CVE-2026-9545.html
curl.se
https://curl.se/docs/CVE-2026-9545.json
curl.se
https://hackerone.com/reports/3752888
hackerone.com
News mentions
1

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