Vulnerability Details CVE-2026-9545
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transfers, and when it makes a second transfer to the same site it has been
replaced by the attacker's impostor machine - without a valid certificate.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.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.004
EPSS Ranking 32.9%
CVSS Severity
CVSS v3 Score 7.5
References
Products affected by CVE-2026-9545
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cpe:2.3:a:haxx:curl:8.11.0
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cpe:2.3:a:haxx:curl:8.11.1
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cpe:2.3:a:haxx:curl:8.12.0
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cpe:2.3:a:haxx:curl:8.12.1
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cpe:2.3:a:haxx:curl:8.13.0
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cpe:2.3:a:haxx:curl:8.14.0
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cpe:2.3:a:haxx:curl:8.14.1
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cpe:2.3:a:haxx:curl:8.15.0
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cpe:2.3:a:haxx:curl:8.16.0
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cpe:2.3:a:haxx:curl:8.17.0
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cpe:2.3:a:haxx:curl:8.18.0