https://bugs.exim.org/show_bug.cgi?id=1684
Bug ID: 1684
Summary: Malformed headers which exceed length spec willingly
passed to remote servers
Product: Exim
Version: 4.80
Hardware: x86
OS: Linux
Status: NEW
Severity: bug
Priority: medium
Component: Transports
Assignee: nigel@???
Reporter: rubin@???
CC: exim-dev@???
The SMTP Spec states that:
> 2.1.1. Line Length Limits
> There are two limits that this standard places on the number of
> characters in a line. Each line of characters MUST be no more than
> 998 characters, and SHOULD be no more than 78 characters, excluding
> the CRLF.
However, if exim gets a message in the queue whose line length is longer than
998 chars it will happily send it to other hosts, thus violating the protocol.
In addition, MANY MTAs (including gmail) will respond to an over-length line
by hanging up on the connection (TCP RST) without any error message. Exim
misclassifies this as a host error (as documented in
http://www.exim.org/exim-html-current/doc/html/spec_html/ch-smtp_processing.html#SECToutSMTPerr)
As a result, sending messages that contain long header lines to a local server
for delivery to a remote site can interrupt delivery of legitimate messages to
that remote site. This has been seen with certain "References" headers.
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