CVE-2026-9546Haxx Curl
NVDCVSS scored by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Vulnerability Summary
A vulnerability in libcurl caused the HTTP `Referer:` header to persist even
when explicitly cleared. While the documentation states that passing NULL to
`CURLOPT_REFERER` suppresses the header, the option failed to clear the
internal state. As a result the previous referrer string was erroneously
reused and sent in subsequent requests, potentially leaking sensitive
information to unintended servers.
when explicitly cleared. While the documentation states that passing NULL to
`CURLOPT_REFERER` suppresses the header, the option failed to clear the
internal state. As a result the previous referrer string was erroneously
reused and sent in subsequent requests, potentially leaking sensitive
information to unintended servers.
CVSS v3.1 Base Metrics — Score 7.5 (HIGH)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:NAttack VectorNetwork
Attack ComplexityLow
Privileges RequiredNone
User InteractionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityNone
AvailabilityNone
Affected & Patched Versions
- Haxx Curl >= 8.18.0 and < 8.21.0
- Haxx Curl 8.21.0
What to do
Prioritize this fix. Exploit code is public, so attacks can follow quickly.
- Check whether you run Haxx Curl and which version.
- Update to a patched version listed above, then confirm the new version.
- Review logs and exposed services for signs of earlier compromise.
Timeline
- Jul 3, 2026Published
- Jul 7, 2026Record last modified
Score, severity and exploitation changes are tracked from the day Watchtower started logging them.
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External References
Data last checked: Nov 15, 2026 03:31 UTC