A parser bug is a flaw in code that reads and interprets structured data, such as PDFs, archives, installers, or image files. Parsers are common in security tools because they must inspect untrusted content from users, email, web downloads, and endpoints.
These bugs matter because a carefully crafted file can drive the parser down an unexpected code path, causing a crash, hang, memory corruption, or sometimes code execution. In defensive software, that can be especially damaging: if an antivirus or content scanner crashes while examining a file, the system may lose visibility exactly when it needs protection most.
Attackers look for parser bugs in file handlers, unpackers, and scanning engines because they often process complex formats at high privilege and with little user interaction. Defenders reduce risk by patching quickly, limiting exposed file types where possible, monitoring repeated scan failures, and treating parser crashes as security incidents rather than harmless glitches.