CVE-2026-11352 curl vulnerability
An issue in curl’s QUIC UDP receive function allows a malicious HTTP/3 server to trigger a remote denial of service against a curl or libcurl client. Because the helper function discards zero-length UDP datagrams before counting them toward the per-call packet budget, a connected QUIC peer can continuously stream empty datagrams to indefinitely stall the client.
Quick answer
haxx curl should be reviewed and updated if it matches the affected versions. The recommended fix is to apply the vendor-supported patched version or the mitigation steps below, then retest the public website with Fixnx.
Who is affected
Affected versions
- curl 8.18.0 through 8.20.0
Fixed versions
- curl 8.21.0 or later
How to fix it
CVE-2026-11352 affects haxx curl. The affected range is curl 8.18.0 through 8.20.0. Update to curl 8.21.0 or later. Treat exposed systems first, especially where systems, apps, containers, and tools that use curl or libcurl can be reached. If you suspect abuse, review logs and rotate secrets that may have been exposed.
- Inventory every haxx curl install and note the exact version.
- Compare each install with the affected range: curl 8.18.0 through 8.20.0.
- Update to curl 8.21.0 or later.
- If you cannot patch today, restrict systems, apps, containers, and tools that use curl or libcurl to trusted users and networks.
- Back up the current configuration before changing production systems.
- Review recent logs for errors, crashes, strange admin activity, or unexpected outbound connections.
- Rotate passwords, tokens, and keys if the system may have been exposed or abused.
- Document the change, owner, date, and final version.
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Verify the fix
- Confirm the installed version now matches the fixed guidance: curl 8.21.0 or later.
- Confirm old affected versions are no longer deployed: curl 8.18.0 through 8.20.0.
- Confirm systems, apps, containers, and tools that use curl or libcurl is limited to the smallest needed group.
- Rerun the relevant Fixnx scan or internal check after the change.
- Save logs, screenshots, or package output as proof of the fix.
Related categories
Trusted references
FAQ
What is affected by CVE-2026-11352?
haxx curl versions listed as affected should be reviewed: curl 8.18.0 through 8.20.0.
What should I fix first?
Start with internet-facing sites, admin panels, login flows, plugins, themes, modules, packages, and systems that process user-controlled input or sensitive data.
How do I confirm the fix worked?
Apply the patched version or mitigation, clear caches where relevant, retest the affected workflow, and run a new Fixnx scan to verify public website exposure signals.
How are Fixnx security risk categories chosen?
Fixnx keeps one canonical risk page and assigns only broad, relevant categories such as ecosystem, technology area, or vulnerability class.