Owasp-modsecurity-crs: RCE detection bypass at PL1

[dune73]

The following bypass was pasted on twitter.

{ 1 }; ;+$u+cat+/etc$u/passwd$u
{ 2 }; ;+$u+cat+/etc$u/passwd+\#

https://twitter.com/spyerror/status/1162826904833089541?s=19

According to @franbuehler, this passes on PL1, but is being detected on PL2.

Type of Issue

RCE rule detection bypass

Description

See above.

Your Environment

CRS 3.1

Confirmation

[X] I have removed any personal data (email addresses, IP addresses,
passwords, domain names) from any logs posted.

[franbuehler]

First command gets the following scores:
individual paranoia level scores: 0, 13, 11, 13

Second command:
individual paranoia level scores: 0, 18, 11, 13

[marcstern]

This evasion technique (and several others) can be defeated with the t:bash transformation - see https://www.approach.be/en/modsecurity.html

[dune73]

If only it would be merged ...

[theMiddleBlue]

IIRC we already talk about that in a meeting (refer to https://www.secjuice.com/web-application-firewall-waf-evasion/). If you agree, I would try to catch this bypass technique in PL1.

[github-actions[bot]]

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[theMiddleBlue]

still in progress...