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vulnerability CVE-2011-2692

libpng: denial of service via sCAL

Synthesis of the vulnerability

An attacker can invite the victim to display a malicious PNG image, in order to generate a denial of service in applications linked to libpng.
Vulnerable systems: Debian, Fedora, libpng, Mandriva Linux, NLD, OES, openSUSE, Solaris, Trusted Solaris, RHEL, SUSE Linux Enterprise Desktop, SLES.
Severity of this threat: 1/4.
Consequences of an attack: denial of service on client.
Pirate's origin: document.
Creation date: 08/07/2011.
Références of this weakness: BID-48618, CERTA-2003-AVI-037, CVE-2011-2692, DSA-2287-1, FEDORA-2011-10928, FEDORA-2011-10954, FEDORA-2011-8844, FEDORA-2011-8867, FEDORA-2011-9336, FEDORA-2011-9343, MDVSA-2011:151, openSUSE-SU-2011:0915-1, RHSA-2011:1103-01, RHSA-2011:1104-01, RHSA-2011:1105-01, SUSE-SU-2011:0916-1, SUSE-SU-2011:0919-1, VIGILANCE-VUL-10820, VU#819894.

Description of the vulnerability

The libpng library is used by several applications to decode or display PNG images.

The sCAL ("Physical Scale") field of a PNG image defines its relative scale. Its format is:
 - one byte: unit (meter)
 - the X axis multiplier, stored as text (for example "2.5")
 - a null byte
 - the Y axis multiplier, stored as text (for example "2.5")

However, if the sCAL field is empty, or if the null byte is missing, the png_handle_sCAL() function tries to read at an invalid memory address.

An attacker can therefore invite the victim to display a malicious PNG image, in order to generate a denial of service in applications linked to libpng.
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