Tried, Tested and Proven

Security Advisory 07-007 – Denial of Service due to a heap smash while parsing CTCP requests

Vulnerability discovery and development:

Portcullis Security Testing Services

Credit for Discovery:

Nico Leidecker of Portcullis Computer Security Ltd discovered this vulnerability. Further research was then carried out.

Affected Systems:

Version 0.3.151 was tested to be vulnerable.


HydraIRC supports CTCP requests. Before showing CTCP request messages on the screen, HydraIRC parses the user input and replaces every percentage character with two of them. It fails to check the length of the resulting string and thereby is prone to a buffer overflow attack.


Since there are more than 506 bytes needed to overwrite important data on the stack and according to the RFC, the full request sent cannot be more than 512 bytes, it is unlikely to find a public server that would be abused for that attack. Nevertheless, an attacker can still crash the victim’s client, if the victim connects to a modified server or a server not compliant to the RFC.


Proof of concept exploit code is available.

Vendor Status:

The vendor has been informed and the vulnerability has been fixed.


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