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Severity: 1/4

Consequences: denial of service of service

Provenance: internet client

Means of attack: 1 attack

Ability of attacker: technician (2/4)

Confidence: confirmed by the editor (5/5)

Diffusion of the vulnerable configuration: high (3/3)

Creation date: 19/06/2009

IMPACTED PRODUCTS

 Apache httpd

DESCRIPTION OF THE VULNERABILITY

When a client connects to the httpd service, he has to send an HTTP request like:
GET / HTTP/1.0
Host: server
Header: etc.

As long as Apache httpd did not receive the full request, it waits at most TimeOut seconds before closing the session.

When MaxClients clients are simultaneously connected on the service, next clients cannot access to the service.

An attacker can therefore open several parallel sessions, in which he sends the request using small fragments, in order to extend the session and to reach MaxClients. Legitimate users then cannot access to the service.

An attacker can therefore exhaust the maximum number of allowed clients on an Apache httpd server, in its default configuration.

The IIS web server uses a different logic and is not impacted by this denial of service. For example, when a new session arrives, the older inactive or incomplete session is closed.

CHARACTERISTICS

Identifiers: 47386, VIGILANCE-VUL-8809

http://vigilance.fr/vulnerability/Apache-httpd-denial-of-service-8809