CVE-2026-6276
Published: 13 May 2026
Summary
CVE-2026-6276 is a high-severity Cleartext Transmission of Sensitive Information (CWE-319) vulnerability in Haxx Curl. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Steal Web Session Cookie (T1539); ranked at the 2.1th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-29928
Vulnerability details
Using libcurl, when a custom `Host:` header is first set for an HTTP request and a second request is subsequently done using the same *easy handle* but without the custom `Host:` header set, the second request would use stale information…
more
and pass on cookies meant for the first host in the second request. Leak them.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Vulnerability causes unintended leakage of session cookies due to stale Host header handling in libcurl, directly facilitating theft of web session cookies.
CVEs Like This One
Affected Assets
Mitigating Controls
Likely Mitigating Controls AI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
Role-based training covers secure transmission methods, mitigating cleartext transmission of sensitive data.
By requiring documented security controls for information exchanges, the control reduces the risk of cleartext transmission of sensitive data.
Mapping transmission actions in data flows helps prevent cleartext transmission of sensitive information.
Settings can enforce secure transmission protocols to prevent cleartext transmission of sensitive data.
Policy addresses secure transport and handling of media to avoid cleartext transmission of sensitive information.
Enforces safeguards against cleartext transmission of CUI when data leaves organizational boundaries to external systems.
Explicit controls and continuous oversight on external system services prevent cleartext transmission of sensitive information over provider-managed channels.
Key-establishment procedures specify secure distribution channels that preclude cleartext transmission of key material.