Opened 3 years ago

Closed 3 years ago

Last modified 3 years ago

#15324 closed enhancement (fixed)

fetchmail-6.4.20 (Security Update)

Reported by: Douglas R. Reno Owned by: ken@…
Priority: elevated Milestone: 11.0
Component: BOOK Version: git
Severity: normal Keywords:


New point version. I haven't looked at the release notes yet, but I did receive an email from the oss-security mailing list (contents in the comments).

TL;DR - Information Disclosure

Change History (4)

comment:1 by Douglas R. Reno, 3 years ago


I have announced fetchmail 6.4.20 today, which fixes the issue shown in 
the security announcement below.

fetchmail 6.4.20 is available from

The source archive is available at:

Detached GnuPG signatures for the respective tarballs are at:

SHA256 hash values for the tarballs:
SHA256(fetchmail-6.4.20.tar.lz)= 497973353c0538216e7d7f2289a21d9acc5edd78f06d7ec008001f4f19e91b11
SHA256(fetchmail-6.4.20.tar.xz)= c82141ae2e8f0039ceb0c5c2eda43c5e93ad0bf7f9c6bb628092b3be74386176

fetchmail-SA-2021-01: DoS or information disclosure logging long messages

Topics:		fetchmail denial of service or information disclosure when logging long messages

Author:		Matthias Andree
Version:	1.1
Announced:	2021-07-28
Type:		missing variable initialization can cause read from bad memory 
Impact:		fetchmail logs random information, or segfaults and aborts, 
		stalling inbound mail
Danger:		low
Acknowledgment:	Christian Herdtweck, Intra2net AG, Tübingen, Germany
		for analysis and report and a patch suggestion

CVE Name:	CVE-2021-36386
Project URL:

Affects:	- fetchmail releases up to and including 6.4.19

Not affected:	- fetchmail releases 6.4.20 and newer

Corrected in:	c546c829 Git commit hash

		2021-07-28 fetchmail 6.4.20 release tarball

0. Release history

2021-07-07	initial report to maintainer
2021-07-28 1.0	release
2021-07-28 1.1	update Git commit hash with correction

1. Background

fetchmail is a software package to retrieve mail from remote POP3, IMAP,
ETRN or ODMR servers and forward it to local SMTP, LMTP servers or
message delivery agents. fetchmail supports SSL and TLS security layers
through the OpenSSL library, if enabled at compile time and if also
enabled at run time, in both SSL/TLS-wrapped mode on dedicated ports as
well as in-band-negotiated "STARTTLS" and "STLS" modes through the
regular protocol ports.

2. Problem description and Impact

Fetchmail has long had support to assemble log/error messages that are 
generated piecemeal, and takes care to reallocate the output buffer as needed.  
In the reallocation case, i. e. when long log messages are assembled that can 
stem from very long headers, and on systems that have a varargs.h/stdarg.h 
interface (all modern systems), fetchmail's code would fail to reinitialize 
the va_list argument to vsnprintf. 

The exact effects depend on the verbose mode (how many -v are given) of 
fetchmail, computer architecture, compiler, operating system and 
configuration.  On some systems, the code just works without ill effects, some 
systems log a garbage message (potentially disclosing sensitive information), 
some systems log literally "(null)", some systems trigger SIGSEGV (signal 
#11), which crashes fetchmail, causing a denial of service on fetchmail's end.

3. Solution

Install fetchmail 6.4.20 or newer.

The fetchmail source code is available from

Distributors are encouraged to review the NEWS file and move forward to 
6.4.20, rather than backport individual security fixes, because doing so 
routinely misses other fixes crucial to fetchmail's proper operation, 
for which no security announcements are issued, or documentation,
or translation updates.

Fetchmail 6.4.X releases have been made with a focus on unchanged user and 
program interfaces so as to avoid disruptions when upgrading from 6.3.Z or 
6.4.X to 6.4.Y with Y > X.  Care was taken to not change the interface 

A. Copyright, License and Non-Warranty

(C) Copyright 2021 by Matthias Andree, <>.
Some rights reserved.

fetchmail-SA-2021-01 © 2021 by Matthias Andree is licensed under CC 
BY-ND 4.0. To view a copy of this license, visit

Use the information herein at your own risk.

END of fetchmail-SA-2021-01

CVE number is CVE-2021-36386.

comment:2 by ken@…, 3 years ago

Owner: changed from blfs-book to ken@…
Status: newassigned

comment:3 by ken@…, 3 years ago

Resolution: fixed
Status: assignedclosed

Updated in e81010f59d0e951e1248ce290e9a03e7b3e2cce3 10.1-703

Security Advisory SA 10.1-085.

comment:4 by Bruce Dubbs, 3 years ago

Milestone: 10.211.0

Milestone renamed

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