CVE-2020-27770 in ImageMagick
Summary
by MITRE • 12/04/2020
Due to a missing check for 0 value of `replace_extent`, it is possible for offset `p` to overflow in SubstituteString(), causing potential impact to application availability. This could be triggered by a crafted input file that is processed by ImageMagick. This flaw affects ImageMagick versions prior to 7.0.8-68.
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Analysis
by VulDB Data Team • 12/12/2020
The vulnerability identified as CVE-2020-27770 represents a critical buffer overflow condition within ImageMagick's string substitution functionality that can lead to application instability and potential denial of service scenarios. This flaw exists in the SubstituteString() function where a crucial validation check for zero values of the replace_extent parameter is absent, creating a scenario where the offset parameter p can experience integer overflow during string processing operations. The vulnerability specifically impacts ImageMagick versions prior to 7.0.8-68, making older installations particularly susceptible to exploitation. The missing validation creates a path where maliciously crafted input files can trigger the overflow condition, potentially leading to unpredictable application behavior and system instability.
The technical implementation of this vulnerability stems from inadequate input sanitization within the string manipulation routines of ImageMagick's image processing pipeline. When the SubstituteString() function processes a crafted input file, it fails to validate whether the replace_extent parameter contains a zero value before proceeding with calculations that determine the offset p. This absence of validation allows the offset calculation to potentially wrap around or exceed the bounds of the allocated memory space, resulting in integer overflow conditions. The flaw operates at the intersection of memory management and input processing, where improper boundary checks in the string substitution algorithm create a condition that can be exploited through carefully constructed input data. This vulnerability aligns with CWE-191, which specifically addresses integer underflow and overflow conditions, and demonstrates how insufficient parameter validation can lead to memory corruption issues.
The operational impact of this vulnerability extends beyond simple denial of service to potentially enable more sophisticated attack vectors that could compromise system availability and stability. When triggered by malicious input files, the integer overflow in the offset calculation can cause the application to crash or behave unpredictably, effectively rendering ImageMagick unavailable for legitimate image processing tasks. This makes the vulnerability particularly dangerous in environments where ImageMagick serves as a core component for image handling, such as web applications, content management systems, or automated processing pipelines. The attack surface is broad since any application that utilizes ImageMagick for processing user-supplied image files could be affected, making this a significant concern for organizations that rely on ImageMagick for their image processing workflows. The vulnerability's impact is consistent with ATT&CK technique T1499.004, which involves network denial of service attacks through application-level resource exhaustion or corruption.
Mitigation strategies for CVE-2020-27770 center on immediate version upgrades to ImageMagick 7.0.8-68 or later, which contain the necessary patches to address the missing validation check for replace_extent parameter. Organizations should also implement input validation measures that filter or sanitize image files before processing, particularly when handling untrusted input from external sources. Additional protective measures include deploying application sandboxing techniques to limit the potential impact of exploitation, implementing monitoring systems to detect unusual application behavior or crashes, and establishing regular security updates and patch management procedures. The fix implemented in the patched version addresses the root cause by introducing proper validation of the replace_extent parameter, ensuring that zero values are properly handled before proceeding with offset calculations. Security teams should also consider implementing network-level controls to restrict access to ImageMagick processing endpoints and establish incident response procedures for handling potential exploitation attempts.