Red Hat ACS Central: SAML assertions can be replayed for repeated authentication tokens

Impact

Central's SAML assertion consumer service does not record used assertion or response identifiers, so a signed, unexpired SAML response can be submitted repeatedly and each submission yields a fresh Central authentication token for the mapped identity. Anyone who captures one such response - from a proxy log, a browser, or a misrouted redirect - holds reusable access to the security console that governs admission control and image policy across the clusters, including GPU clusters. That console is a control point for what workloads are allowed to run, so the identity it hands out matters more than a typical web login.

Who can reach it

Network reachability to Central's SAML ACS endpoint plus possession of a valid, unexpired signed SAML response. No prior authentication to Central is needed; obtaining the assertion is the hard part, which is why the record rates attack complexity high.

What to do

Apply the fixed RHACS builds shipped in RHSA-2026:85932 (4.10) and RHSA-2026:92342 (4.11 for IBM Z/LinuxONE) and restart Central; this is a control-plane service restart, not a node operation. Until then, invalidating captured assertions is not possible, so shorten IdP assertion lifetimes and audit Central session issuance.

References

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