CVE-2026-55458
Description
A flaw was found in Caddy's reverse proxy module. When processing protocol upgrade responses, the proxy fails to properly remove hop-by-hop headers intended only for intermediate connections. A malicious or compromised upstream server can exploit this flaw to forward restricted connection headers across the proxy boundary. This can cause clients to process untrusted connection instructions, potentially leading to unintended connection behavior.
Statement
This vulnerability is classified as having a Low impact because exploitation depends on an attacker already possessing administrative control or compromise over an upstream backend service. In typical enterprise architectures, reverse proxies route traffic to trusted internal services, which significantly reduces the likelihood of encountering rogue protocol upgrade responses. Moreover, the scope of the vulnerability is limited to the propagation of unstripped transport headers to connecting clients, without directly allowing remote command execution, privilege elevation, or access to server-side memory.
Mitigation
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.
Understanding the Weakness (CWE)
Integrity
Technical Impact: Unexpected State
Frequently Asked Questions
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