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Mallory
CriticalPublic exploit

Unexpected session resumption in Go crypto/tls

IdentifiersCVE-2025-68121CWE-295· Improper Certificate Validation

In Go's crypto/tls, session resumption can incorrectly succeed if the tls.Config trust settings are changed between the original handshake and a resumed handshake. Specifically, if the underlying Config has its ClientCAs or RootCAs fields mutated after the initial handshake, the resumed handshake may be accepted even though a full handshake under the updated configuration should fail. The issue can arise when an application calls Config.Clone() and then mutates the returned configuration, or when it uses Config.GetConfigForClient and returns configurations whose CA pools differ over time. As a result, a client may resume a session with a server it would no longer trust, or a server may resume a session with a client it would no longer accept under mutual TLS policy.

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ANALYST BRIEF

Impact, mitigation & remediation

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Impact

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This flaw can bypass expected certificate validation and trust-policy changes during TLS session resumption. It may allow continued use of previously established sessions after ClientCAs or RootCAs have changed, weakening server authentication or mutual TLS enforcement. In practice, this can permit unauthorized or unintended resumed connections that should have been rejected under the current CA configuration, reducing the effectiveness of trust-anchor rotation, client-auth policy changes, or other certificate validation controls.

Mitigation

If you can’t patch tonight, do this now.

Do not mutate ClientCAs or RootCAs on tls.Config objects that may participate in resumable sessions. Avoid patterns where Config.Clone() results share mutable CA state with active configurations, and ensure GetConfigForClient does not return configs whose trust stores can change during the lifetime of resumable sessions. Where dynamic CA/trust changes are required and an upgrade is not yet possible, disable TLS session resumption for affected endpoints to force full handshakes under current validation policy.

Remediation

Patch, then assume compromise.

Upgrade to a fixed Go release that corrects crypto/tls session resumption behavior for mutated ClientCAs/RootCAs. The provided advisory context indicates patched Go versions include 1.25.7 or 1.24.13 for this CVE. Downstream products statically linking affected Go runtime/library versions should also be rebuilt or upgraded against a fixed Go toolchain.
PUBLIC EXPLOITS

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VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType
GolangGoapplication
Rocky LinuxGo-Fdo-Clientapplication
Rocky LinuxGo-Fdo-Serverapplication
Rocky LinuxImage-Builderapplication
Rocky LinuxOsbuild-Composerapplication
TraefikTraefikapplication

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Detection signatures

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Vendor-by-vendor mapping

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Social activity28

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