CVE-2026-9545
CVE-2026-9545 is a high-severity vulnerability in Haxx Curl with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low.
Key facts
- Severity: High (CVSS 3.x base score 7.5)
- EPSS exploit prediction: 0% (23rd percentile)
- Actively exploited: Not listed in CISA KEV
- Affected product: Haxx Curl
- Published:
- Last modified:
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uses a proper HTTP/3 server for the initial transfers, and when it makes a second transfer to the same site it has been replaced by the attacker's impostor machine - without a valid certificate.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.
Frequently asked questions
- What is 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uses a proper HTTP/3 server for the initial transfers, and when it makes a second transfer to the same site it has been replaced by the attacker's impostor machine - without a valid certificate.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.
- How severe is CVE-2026-9545?
- CVE-2026-9545 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity none, and availability none.
- Is CVE-2026-9545 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (23rd percentile), an estimate of the probability of exploitation in the next 30 days.
- What products are affected by CVE-2026-9545?
- CVE-2026-9545 affects Haxx Curl. See the affected-products list for the exact vulnerable versions.
- How do I fix CVE-2026-9545?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
- When was CVE-2026-9545 published?
- CVE-2026-9545 was published on 2026-07-03 and last updated on 2026-07-07.
References
- https://curl.se/docs/CVE-2026-9545.html
- https://curl.se/docs/CVE-2026-9545.json
- https://hackerone.com/reports/3752888
Affected products (1)
- cpe:2.3:a:haxx:curl:*:*:*:*:*:*:*:*
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