CVE-2018-11576

Vulnerability

A heap-based buffer over-read vulnerability exists in GifIndexToTrueColor in ngiflib.c at line 808 in MiniUPnP ngiflib version 0.4 [1][2]. The flaw occurs when the function accesses memory beyond the bounds of a heap-allocated buffer during GIF image decoding, specifically when processing a malformed GIF file. The issue is triggered during the DecodeGifImg function call chain, as shown in AddressSanitizer reports [2].

Exploitation

An attacker can trigger the vulnerability by supplying a specially crafted GIF file to an application that uses ngiflib for image processing. No authentication or special privileges are required beyond the ability to provide input to the application. The out-of-bounds read occurs in the GifIndexToTrueColor function when it reads pixel color indices from a heap buffer that is smaller than expected [2]. The exact steps involve loading the malformed GIF via LoadGif and then decoding it [1][2].

Impact

A successful exploit can lead to a heap-based buffer over-read, potentially causing information disclosure (reading adjacent heap memory) or a denial of service (crash) due to reading invalid memory. The vulnerability could also be leveraged for more severe impacts if an attacker can control the over-read data to influence program behavior.

Mitigation

As of the publication date, no official fix has been released by the maintainers. The ngiflib repository issue [2] documents the vulnerability but does not include a patch. Users should consider disabling use of ngiflib in applications that process untrusted GIF files until a patch is available and applied.