Security: CVE-2026-58047 HTTP Request Smuggling

Situation

A vulnerability in the cPanel web server allows manipulation of cpsrvd responses under limited conditions.

Affected Product Versions

Impact

In some situations, an unauthenticated remote attacker may be able to manipulate responses delivered to other users on the same server. 

Call to action

Update to the latest patched version: How do I update cPanel/WHM?

Mitigation

Servers that cannot immediately upgrade can disable cpsrvd backend connection reuse as a temporary workaround. To do so, run the following commands as the root user:

# echo 'cpsrvd_keepalives_disabled=1' >> /var/cpanel/cpanel.config 
# pkill -9 cpsrvd
# /usr/local/cpanel/scripts/restartsrv_cpsrvd

Note: This forces a new TCP+TLS connection per request on ports 2083, 2087, and 2096, which increases latency and CPU usage on busy servers. Make sure to revert this change after upgrading by setting the value to 0 and restarting cpsrvd.

To revert that change, run the following commands as the root user:

# sed -i 's/cpsrvd_keepalives_disabled=1/cpsrvd_keepalives_disabled=0/' /var/cpanel/cpanel.config
# pkill -9 cpsrvd
# /usr/local/cpanel/scripts/restartsrv_cpsrvd

Acknowledgements

WebPros thanks Vincent55 Yang for responsibly disclosing this issue.