Back

HIGH

varnish: denial of service via colon-starting reason phrase

Published Aug 11, 2022

Description

In Varnish Cache 7.0.0, 7.0.1, 7.0.2, and 7.1.0, it is possible to cause the Varnish Server to assert and automatically restart through forged HTTP/1 backend responses. An attack uses a crafted reason phrase of the backend response status line. This is fixed in 7.0.3 and 7.1.1.

Affected products

Remediation

Red Hat mitigation

As mentioned in the upstream security advisory, If upgrading Varnish is not possible, it is possible to mitigate the problem by adding the following snippet at the beginning of the vcl_backend_response VCL function: ``` sub vcl_backend_response { set beresp.status = beresp.status; } ``` By setting the status code to itself as described above, the reason field will automatically be reset to the standard value for the given status code, or “Unknown HTTP Status” if no standard value exists for that code. This would overwrite any existing attack content in the reason field.

Metrics

References (8)

Change history (0)

No recorded changes yet.

Sources
CVE.org / MITRE
Status PUBLISHED
Assigner mitre
Published Aug 11, 2022
Updated Oct 20, 2025
Reserved Aug 11, 2022
CISA Vulnrichment
Updated Oct 20, 2025
NVD
Status Modified
Modified Jun 17, 2026
Red Hat
Severity Moderate
Public date Aug 9, 2022