CVE-2015-5522

What it actually does

Heap-based buffer overflow in the ParseValue function in lexer.c triggered by command characters in href attributes, allowing memory corruption that leads to application crashes.

Why it matters to the business

Organizations relying on vulnerable HTML Tidy versions across Linux distributions and Apple platforms risk denial-of-service outages in content sanitization, web scraping, or HTML processing pipelines, with elevated urgency due to the flaw's age and public exploit availability despite low EPSS.

How an attack unfolds

An attacker crafts an HTML payload containing a malicious href attribute embedding a command character, delivers it to a target application using a vulnerable tidy parser (pre-4.9.31), and triggers the ParseValue overflow to crash the process; public exploits have been available since 2015 with no named threat actor campaigns noted.

How to fix it

Upgrade all instances of tidy to version 4.9.31 or later; apply available patches for downstream packages in Ubuntu, Debian, and Apple ecosystems where provided.

How to confirm the fix worked

Confirm installed tidy version meets or exceeds 4.9.31, recompile from verified sources if needed, and test with crafted href payloads to ensure no crash occurs.

Typical attack path

1. Locate services or dependencies using vulnerable tidy versions on affected platforms such as Ubuntu, Debian, or Apple OSes
2. Craft HTML input with specially formatted href containing command characters
3. Submit the payload to the tidy parser via web forms, APIs, or file processing
4. Trigger heap overflow resulting in denial of service

How to detect it

Search application and system logs for tidy process crashes during HTML parsing, review input logs for anomalous href attributes containing control characters, and correlate with any sudden service restarts since public exploits exist.

What your security team should do

• Immediately inventory and update all tidy deployments given the 2015 publication date and ExploitAvailable status
• Prioritize patching in high-dependency environments due to ecosystem prevalence across multiple OS distributions
• Implement input validation around HTML processing to reduce exposure until upgrades complete
• Review and remove any remaining pre-4.9.31 binaries from build pipelines and containers