The png_format_buffer function in pngerror.c in libpng 1.0.x before 1.0.55, 1.2.x before 1.2.45, 1.4.x before 1.4.8, and 1.5.x before 1.5.4 allows remote attackers to cause a denial of service (application crash) via a crafted PNG image that triggers an out-of-bounds read during the copying of error-message data. NOTE: this vulnerability exists because of a CVE-2004-0421 regression. NOTE: this is called an off-by-one error by some sources.
CWE-125 - Out-of-Bounds Read
Out-of-bounds read is a vulnerability that allows access to memory beyond the authorized accessible location. Such a vulnerability compromises the confidentiality of the trusted environment in the application and enables an attacker to launch further attacks by leveraging the exposed information.