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TLS Server Impersonation via Compromised Intermediate Certificates in Perl Mozilla::CA
Mozilla::CA versions before 20261020 for Perl include the emSign ECC Root CA - G3 root certificate, which provides a trust path for intermediate certificates whose private keys are publicly available. An attacker able to intercept or redirect client traffic can use these keys to impersonate a TLS server to clients relying on the affected trust store. Exposure depends on the CA store actually selected: IO::Socket::SSL, commonly used by LWP, HTTP::Tiny, and other Perl clients, normally checks OpenSSL's default certificate locations before falling back to Mozilla::CA. Configuration and environment variables can override this selection.
What it means and what to do now: patch path, interim mitigations, and the assume-compromise checklist.
What an attacker gets, and what they’ve been doing with it.
Successful exploitation compromises the confidentiality and integrity of affected TLS communications through server impersonation and man-in-the-middle interception or modification. Sensitive data transmitted by clients may be exposed, and server responses may be altered. No direct availability impact is identified.
If you can’t patch tonight, do this now.
As an interim measure, configure affected clients to use a CA store that excludes emSign ECC Root CA - G3. Verify the effective CA-store selection rather than assuming Mozilla::CA is used, because IO::Socket::SSL normally prioritizes OpenSSL's default certificate locations.
Patch, then assume compromise.
Upgrade Mozilla::CA to version 20261020 or later when its certificate bundle is used. For clients using the operating system CA store, install the operating system vendor's updates addressing this incident. Verify that each client actually uses the updated trust store, accounting for configuration and environment-variable overrides. Some distribution packages are identified as not receiving a vendor patch; an upstream fixed release does not establish that a corresponding distribution update is available.
No valid public exploits. Mallory filtered out 1 candidate as fakes, detection scripts, or README-only repos.
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
3 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.