CVE-2021-21067 in Photoshop
Summary
by MITRE • 03/13/2021
Adobe Photoshop versions 21.2.5 (and earlier) and 22.2 (and earlier) are affected by an Out-of-bounds Write vulnerability in the CoolType library. An unauthenticated attacker could leverage this vulnerability to achieve arbitrary code execution in the context of the current user. Exploitation of this issue requires user interaction in that a victim must open a malicious file.
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Analysis
by VulDB Data Team • 04/01/2021
Adobe Photoshop contains a critical out-of-bounds write vulnerability within its CoolType font rendering library that affects versions 21.2.5 and earlier, as well as 22.2 and earlier. This flaw resides in the font processing component responsible for handling various font formats including TrueType and OpenType files. The vulnerability manifests when the application processes maliciously crafted font files that contain malformed data structures within their metadata or glyph definitions. The out-of-bounds write occurs during the font rendering process where the application attempts to write data beyond the allocated memory buffer designated for font metrics and rendering information.
The technical exploitation of this vulnerability requires an attacker to craft a specially designed font file that triggers the buffer overflow condition when Photoshop attempts to render the font. This type of vulnerability maps directly to CWE-787: Out-of-bounds Write which is classified as a critical weakness in the Common Weakness Enumeration catalog. The attack vector requires user interaction since victims must open the malicious file within Photoshop for the exploit to be triggered. This user interaction requirement aligns with the ATT&CK technique T1203: Exploitation for Client Execution which describes how adversaries can leverage software vulnerabilities to execute malicious code through user interaction with compromised applications.
The operational impact of this vulnerability is severe as successful exploitation could allow remote code execution with the privileges of the current user. This means that an attacker who successfully delivers a malicious font file could potentially gain full control over the victim's system, including the ability to install malware, modify files, or establish persistence mechanisms. The vulnerability affects the core font rendering functionality that is commonly used when opening various file types including images, documents, and presentations that may contain embedded fonts. The CoolType library is extensively used throughout Photoshop's interface and document processing, making this a particularly dangerous flaw.
Organizations should prioritize immediate patching of affected Photoshop versions to mitigate this vulnerability. Adobe has released security updates addressing this issue in newer versions of Photoshop, and administrators should ensure all users are updated to the latest available versions. Additional mitigations include implementing strict file validation policies that prevent opening untrusted font files, disabling automatic font loading in applications where possible, and educating users about the risks of opening unknown or untrusted files. Network-based protections such as intrusion prevention systems can also be configured to detect and block known malicious font file patterns, though these measures are not foolproof given the sophisticated nature of such exploits. The vulnerability demonstrates the critical importance of keeping creative software applications updated, as font processing libraries often contain complex code that can be prone to memory safety issues.