CVE-2017-8105

What it actually does

Heap-based buffer overflow in t1_decoder_parse_charstrings allows an out-of-bounds write during Type 1 font charstring parsing.

Why it matters to the business

Remote attackers can achieve arbitrary code execution on systems that process untrusted fonts, risking full host compromise, data theft, or ransomware deployment; the flaw affects many applications embedding FreeType and has remained unpatched in some downstream packages for years.

How an attack unfolds

An attacker crafts a malicious Type 1 font containing oversized or malformed charstrings, delivers it via network or file to any application using the vulnerable FreeType library, and triggers t1_decoder_parse_charstrings to overflow the heap buffer and overwrite adjacent memory for code execution.

How to fix it

Upgrade FreeType to a build containing commit 069083cccd73d1d68da68116c8d050bb62cdfe0e or later; for moodle (Bitnami) deployments upgrade to version 3.5.18 or newer. Rebuild and redeploy any statically linked applications. Remove or sandbox legacy font handling paths until patches are applied.

How to confirm the fix worked

Verify installed FreeType version or commit hash against the fixed commit; run regression tests that exercise Type 1 font parsing with the original proof-of-concept corpus; confirm absence of the vulnerable t1decode.c code path via source or binary analysis.

Typical attack path

1. Identify a target application or service that renders or parses fonts with the vulnerable FreeType version
2. Prepare a specially crafted Type 1 font file that triggers the buffer overflow in t1_decoder_parse_charstrings
3. Deliver the font to the victim (web page, document attachment, or network protocol)
4. Trigger font processing to execute the overflow and gain control of the process
5. Escalate privileges or move laterally as needed

How to detect it

Search application and system logs for crashes or memory-corruption signals while processing Type 1 fonts; inspect process memory dumps or core files for heap corruption patterns near font parsing routines; review file-access logs for unexpected .pfb or .pfa files introduced around the time of any anomalous process behavior.

What your security team should do

• Immediately inventory all systems and containers that ship or link FreeType and schedule upgrades
• Prioritize patching internet-facing services that accept user-supplied fonts or documents
• Apply least-privilege sandboxing around font-rendering processes
• Monitor EPSS and KEV feeds for any future increase in observed exploitation