CVE-2021-40709 in Photoshop
Summary
by MITRE • 09/28/2021
Adobe Photoshop versions 21.2.11 (and earlier) and 22.5 (and earlier) are affected by a Buffer Overflow vulnerability when parsing a specially crafted SVG file. 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 • 10/03/2021
Adobe Photoshop versions 21.2.11 and earlier as well as 22.5 and earlier contain a critical buffer overflow vulnerability designated as CVE-2021-40709 that manifests during the parsing of specially crafted svg files. This vulnerability resides within the application's handling of vector graphics format inputs and represents a classic stack-based buffer overflow condition that occurs when the software attempts to write data beyond the allocated memory boundaries. The flaw specifically affects the svg parsing engine which fails to properly validate input lengths and boundaries when processing maliciously constructed vector graphics. The vulnerability is categorized under CWE-121 as a stack-based buffer overflow, which is a well-documented weakness that has been exploited in numerous security incidents throughout the industry. The exploitation of this vulnerability requires a user to open a maliciously crafted svg file, making it a client-side attack vector that relies on social engineering or phishing techniques to deliver the payload. This requirement for user interaction places the vulnerability in the ATT&CK framework under technique T1203 - Exploitation for Client Execution, which specifically targets applications that process user-controllable input. The impact of successful exploitation allows an unauthenticated attacker to execute arbitrary code with the privileges of the current user, effectively providing a complete compromise of the victim's system. This represents a significant elevation of privilege vulnerability since the attacker can potentially gain access to sensitive user data, install additional malware, or establish persistent access to the compromised system.
The technical implementation of this buffer overflow occurs when Photoshop attempts to parse svg elements that contain oversized or malformed data structures that exceed the allocated buffer space. During the parsing process, the application fails to perform adequate bounds checking on the input data, allowing maliciously constructed svg files to overflow the intended buffer and overwrite adjacent memory regions. The vulnerability is particularly concerning because svg files are commonly used for web graphics and can be embedded in various documents and web pages, making them a popular attack vector for delivering malicious payloads. When the vulnerable application processes these crafted files, the buffer overflow can corrupt critical memory structures including stack canaries, return addresses, and function pointers, which can then be manipulated to redirect program execution flow. The vulnerability's exploitation requires careful crafting of the svg file to ensure that the buffer overflow overwrites the return address on the stack, allowing the attacker to control the instruction pointer and redirect execution to malicious code. This type of attack is commonly classified as a stack-based buffer overflow that can be exploited through Return Oriented Programming (ROP) or directly injecting shellcode into the process memory space.
The operational impact of CVE-2021-40709 extends beyond simple code execution, as it represents a complete compromise of the user's system environment. Attackers can leverage this vulnerability to establish persistent access through various means including installing backdoors, creating new user accounts, or deploying additional malware components. The vulnerability affects users who frequently work with vector graphics or open files from untrusted sources, making it particularly dangerous in enterprise environments where users may unknowingly open malicious attachments or download compromised graphics files. The requirement for user interaction does not mitigate the risk significantly since social engineering techniques can effectively bypass user awareness, especially when the malicious file appears legitimate or is delivered through trusted channels. Organizations using affected versions of Adobe Photoshop should consider implementing network-based mitigations such as web application firewalls or content filtering solutions that can detect and block suspicious svg file content. The vulnerability also impacts users who work with web content, as svg files are commonly embedded in web pages and documents, making the attack surface much broader than initially apparent. Security professionals should monitor for indicators of compromise including unusual process behavior, network connections to known malicious domains, or unexpected file modifications that could result from exploitation of this vulnerability. The exploitability of this vulnerability is enhanced by the fact that it can be triggered through multiple vectors including direct file opening, drag-and-drop operations, or even automatic loading when applications attempt to preview svg content.
Mitigation strategies for CVE-2021-40709 should include immediate patching of affected Adobe Photoshop versions to the latest releases that contain the necessary security fixes. Adobe has released patches for this vulnerability in subsequent versions of their software, and users should ensure they are running patched versions to eliminate the risk of exploitation. Organizations should implement strict file validation policies that prevent users from opening svg files from untrusted sources or that automatically scan svg content for known malicious patterns. The implementation of application whitelisting solutions can prevent execution of unsigned or untrusted svg files, while sandboxing techniques can isolate the processing of potentially malicious graphics files. Network-based protections such as intrusion detection systems and content filtering solutions should be configured to detect and block suspicious svg file transfers or requests. Users should be educated about the risks of opening svg files from unknown sources and should be trained to recognize phishing attempts that might deliver malicious graphics files. Security monitoring should include detection of unusual file access patterns, process execution from temporary directories, and network connections that might indicate successful exploitation attempts. Additionally, system administrators should consider disabling automatic preview features for svg files and implementing strict access controls to limit the privileges of users who might inadvertently trigger the vulnerability through normal application usage. The vulnerability also highlights the importance of regular security updates and patch management procedures, as this type of flaw can remain undetected for extended periods if proper maintenance protocols are not followed.