CVE-2010-2883

What is Adobe Reader and CoolType Font Rendering?

Adobe Acrobat and Adobe Reader support embedded fonts in PDF documents, including OpenType and TrueType fonts. CoolType is Adobe's proprietary font rendering library — a DLL (CoolType.dll) included with Reader and Acrobat that handles parsing and rendering of embedded fonts. CoolType processes complex binary font format structures including SING (Smart Independent Glyphs) tables, which define glyph substitution rules for languages with complex typographic requirements. The CoolType font parser was a rich attack surface due to the complexity of font format specifications and the historical expectation that font data would be trusted input from PDF documents.

Overview

CVE-2010-2883 is a high-severity stack-based buffer overflow vulnerability (CWE-787, CVSS 7.3) in Adobe Acrobat and Reader's CoolType font rendering library. A specially crafted PDF containing a malformed SING font table causes a stack overflow in CoolType.dll, enabling code execution when the PDF is opened. This vulnerability was actively exploited as a zero-day in targeted attacks before Adobe released the patch in out-of-band Security Bulletin APSB10-21. CISA added to KEV in June 2022.

Affected Versions

Note: All Adobe Reader and Acrobat versions prior to version 11 are end-of-life.

Technical Details

The stack-based buffer overflow (CWE-787: Out-of-Bounds Write) exists in CoolType.dll's processing of the SING (Smart Independent Glyphs) table within embedded OpenType fonts. The SING table contains complex linguistic data for font rendering; the vulnerable code copies a field from the SING table into a stack-allocated buffer without validating that the field length fits within the buffer's size.

A PDF containing a crafted font with an oversized SING table field causes the buffer copy to overwrite adjacent stack data — including the saved return address. By controlling the content written beyond the buffer boundary, an attacker can redirect program execution to injected code.

The CVSS score's Local attack vector (AV:L) and Low Privilege Required (PR:L) is unusual for what appears to be a drive-by PDF exploit. This metric combination reflects the NVD's assessment of the exploitation prerequisites at the application level rather than the delivery mechanism. In practice, malicious PDFs were delivered via email and web downloads — the user interaction (UI:R) is opening the PDF in Reader, not any local privilege escalation step.

The zero-day exploitation before the patch suggests use by sophisticated threat actors with access to CoolType vulnerability research. Adobe's out-of-band patch (released outside the normal quarterly cycle) reflected the severity of confirmed in-the-wild exploitation.

Discovery

Identified through analysis of malicious PDFs used in targeted attacks. Security researchers reverse-engineered the exploit samples to identify the vulnerable code path in CoolType.dll. Adobe acknowledged the zero-day exploitation and released APSB10-21 as an emergency out-of-band patch approximately four weeks after the initial reports — a tight timeline that reflected both the severity of confirmed exploitation and Adobe's improved emergency response processes following the lessons of multiple Reader zero-days in 2009-2010.

Exploitation Context

Adobe Reader font parsing vulnerabilities were consistently among the most reliable exploit delivery mechanisms in targeted attacks:

• Zero-day targeted attacks: The pre-patch exploitation suggests use by sophisticated actors in targeted campaigns — the exploit technique (CoolType SING table overflow) required deep knowledge of Adobe's proprietary font library, pointing to dedicated vulnerability research by well-resourced threat actors.
• Criminal exploit kit adoption: After public disclosure and patch release, the exploit was analyzed, reimplemented, and incorporated into criminal exploit kits. Legacy Reader installations encountering malicious PDFs on the web were silently compromised.
• PDF trust assumption: Users in this era commonly opened PDF attachments from unknown senders without suspicion — PDF was seen as a "safe" format. This trust made Reader exploits extremely effective as phishing attachment vectors.
• Persistent patching lag: Adobe Reader operated outside most enterprise patch management systems. Organizations relying on manual Reader updates maintained vulnerable installations for months after patches were available.
• Companion to Reader JavaScript exploits: Font parsing vulnerabilities like CVE-2010-2883 provided a reliable alternative to JavaScript-based exploits when JavaScript was disabled in Reader's security settings.

Remediation

1. Apply APSB10-21: Upgrade to Adobe Reader/Acrobat 9.4 or 8.2.5 per the security bulletin.
2. Upgrade to current Adobe Reader: All Reader 8.x and 9.x versions are end-of-life. Install Adobe Acrobat Reader DC (current version).
3. Disable JavaScript: Even if exploiting via font parsing, disabling JavaScript in Reader (Edit > Preferences > JavaScript) removes companion attack vectors.
4. Enable Protected Mode: Newer Reader versions run in Protected Mode (sandboxed) — ensure this is enabled for all users.
5. Use browser PDF viewers: Chrome, Firefox, and Edge include built-in PDF renderers that do not use Adobe CoolType and are not affected by CoolType vulnerabilities.