GLSA 200405-07: Exim verify=header_syntax buffer overflow

Title:Exim verify=header_syntax buffer overflow
Bugs: #50217


When the verify=header_syntax option is set, there is a buffer overflow in Exim that allows remote execution of arbitrary code.


Exim is an highly configurable message transfer agent (MTA) developed at the University of Cambridge.

Affected packages

Package Vulnerable Unaffected Architecture(s)
mail-mta/exim <= 4.33 >= 4.33-r1 All supported architectures


When the option "verify = header_syntax" is used in an ACL in the configuration file, Exim is vulnerable to a buffer overflow attack that can be triggered remotely by sending malicious headers in an email message. Note that this option is not enabled in Exim's default configuration file.


This vulnerability can be exploited to trigger a denial of service attack and potentially execute arbitrary code with the rights of the user used by the Exim daemon (by default this is the "mail" user in Gentoo Linux).


Make sure the verify=header_syntax option is not used in your exim.conf file.


All users of Exim should upgrade to the latest stable version:

    # emerge sync

    # emerge -pv ">=mail-mta/exim-4.33-r1"
    # emerge ">=mail-mta/exim-4.33-r1"



This GLSA and any updates to it are available for viewing at the Gentoo Security Website:


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