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Exim Vulnerability Puts More than 500,000 Email Servers at High Risk

A critical vulnerability with Exim email servers put’s more than 500,000 servers at risk. The bug affects all the version of Exim from the first commit to last 3.x release.

The Vulnerability resides with b64decode function in the SMTP listener. When the provided input is not a valid base64 string it consumes additional bytes while decoding which causes the one-byte heap overflow.