JFrog Security Research
< Back

XRAY-228464 - Apache httpd mod_sed DoS

CVE-2022-30522 | CVSS 7.5

JFrog Severity:medium

Discovered ByBrian Moussalliof the JFrog Security Research Team

Published 9 Jun, 2022 | Last updated 9 Jun, 2022

Very large input data may cause Apache's mod_sed filter to abort, resulting in a denial of service ​

Apache's mod_sed filter module

Apache (, 2.4.53], fixed in 2.4.54 ​

The Apache HTTP Server is the most popular web server in the world. One of its main features is the possibility to use filter modules for various purposes.

One such module, mod_sed, provides the webmaster the same possibilities offered by GNU's stream editor, sed. This module can be installed as an InputFilter or as an OutputFilter if someone wishes to edit requests or responses before they're processed by the server, or before being sent back to the client.

A bug found in mod_sed's buffer manipulation logic may cause to the abort of the process handling the HTTP request. This occurs when the mod_sed module is required to to handle inputs larger than 2GB of data.

An Apache deployment is vulnerable to remote exploitation if -

  1. The server enables mod_sed in httpd.conf -

    LoadModule sed_module /usr/lib/apache2/modules/mod_sed.so
  2. The server configures mod_sed to perform any kind of processing on incoming requests, by using AddInputFilter. For example -

    <Directory />
        AllowOverride none
        Require all denied
        AddInputFilter Sed html
        InputSed "s/\(.)/Z/g"

​ (note that the vulnerability can be triggered for any InputSed patterm)

python -c 'print("A")*(2*2**30)' | curl -X POST -d@- http://host

The LimitRequestBody configuration directive can be used to limit POST requests' sizes. We recommend setting the limit to 1GB of data or less in httpd.conf: LimitRequestBody 1073741824

Apache advisory

(JFrog) CVE-2022-30522 – Denial of Service (DoS) Vulnerability in Apache httpd “mod_sed” filter

< Back