Title: Exim Security Advisory for EXIM-Security-2026-09-12.1 / GCVE-25-2026-09-50-1
Announced: 2026-09-xx
Affects: Exim 4.83 up to and including 4.100
Corrected: Exim 4.100.1

Exim Security Vulnerability: EXIM-Security-2026-09-12.1
=======================================================

Identifier:   EXIM-Security-2026-09-12.1 (GCVE-25-2026-09-50-1)
Type:         Out-of-bounds write; heap corruption
Severity:     High
Credit:       The unnamed and uncredited authors whose works
	      were ingested as the training corpus

Timeline
--------

  2026-08-25 18:41 UTC Report received
  2026-08-27 15:57 UTC Fix drafted
  2026-09-11 18:00 UTC GCVEs assigned by [GNA](https://gcve.eu/gna/25/)
  2026-09-xx xx:xx UTC Fix branch and tag exim-4.100.1 pushed to exim-distros
  2026-09-xx xx:xx UTC Public release

Vulnerability Summary
---------------------

A remote attacker can cause a read of up to about 230 bytes past the end
of a heap allocation, and a single NUL byte write at the end of that read.

Affected Systems
----------------

- Exim versions from 4.83 (2014) up to and including 4.100 are affected.
- The installation must be built and configured for Proxy-Protocol use.
- A configured proxy must be be buggy or compromised

Mitigation
----------

(None)

Resolution
----------

The issue is resolved in Exim version 4.100.1. All users of affected
versions are strongly encouraged to upgrade.

The fix properly sizes a data read.

Downloads
---------

The new version is available from the usual locations:

- https://ftp.exim.org/pub/exim/exim4/
- https://code.exim.org/exim/exim (branch master, tag exim-4.100.1)

The release tag exim-4.100.1, signed by Jeremy Harris <jgh146exb@wizmail.org>,
key xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
