CVE-2017-7961 in libcroco
Summary
by MITRE
The cr_tknzr_parse_rgb function in cr-tknzr.c in libcroco 0.6.11 and 0.6.12 has an "outside the range of representable values of type long" undefined behavior issue, which might allow remote attackers to cause a denial of service (application crash) or possibly have unspecified other impact via a crafted CSS file. NOTE: third-party analysis reports "This is not a security issue in my view. The conversion surely is truncating the double into a long value, but there is no impact as the value is one of the RGB components.
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Analysis
by VulDB Data Team • 07/03/2024
The vulnerability identified as CVE-2017-7961 resides within the cr_tknzr_parse_rgb function in the libcroco library version 0.6.11 and 0.6.12, specifically in the cr-tknzr.c source file. This issue represents a classic undefined behavior scenario that arises when processing RGB color values within CSS parsing operations. The flaw manifests when the function encounters RGB color components that exceed the representable range of the long data type during conversion from double precision floating point values. This undefined behavior creates potential for unpredictable application states and system instability.
The technical implementation of this vulnerability stems from improper type handling during CSS color parsing operations where floating point values representing RGB components are converted to long integers without proper bounds checking or validation. When a crafted CSS file contains RGB values that, when processed, result in values outside the range of representable values for the long type, the undefined behavior can trigger memory corruption patterns or arithmetic exceptions. The vulnerability specifically impacts the conversion process where double precision values are truncated to long integers, creating a scenario where the mathematical operations may not behave as expected according to the c standard. This undefined behavior falls under CWE-369, which addresses division by zero and related arithmetic errors that can lead to unpredictable system states.
From an operational perspective, this vulnerability presents a significant risk for applications that utilize libcroco for CSS processing, particularly web browsers, content management systems, and other software that parses CSS files. Remote attackers can exploit this weakness by crafting malicious CSS files that contain RGB values triggering the conversion overflow condition. The primary impact manifests as denial of service through application crashes, but the undefined behavior nature suggests potential for more severe consequences including memory corruption that could be leveraged for code execution under certain circumstances. The vulnerability affects any system processing untrusted CSS content, making it particularly dangerous in web environments where CSS files can be dynamically loaded from external sources.
The mitigation strategies for CVE-2017-7961 should focus on immediate library updates to versions that address the undefined behavior in the cr_tknzr_parse_rgb function. System administrators and developers should implement input validation measures that prevent malformed CSS content from reaching the vulnerable parsing functions, particularly in web applications that process user-generated content. Additionally, implementing proper bounds checking and type conversion validation within the CSS parsing pipeline can help detect and reject potentially malicious RGB values before they trigger the undefined behavior. Organizations should also consider deploying intrusion detection systems that monitor for unusual patterns in CSS processing that might indicate exploitation attempts. The ATT&CK framework categorizes this vulnerability under T1210 exploitation of remote services and T1059 command and scripting interpreter, as it represents a vector for remote code execution through malformed input processing. Regular security audits and dependency updates remain crucial for preventing exploitation of similar undefined behavior vulnerabilities in other libraries and components.
The third-party analysis suggesting this is not a security issue due to truncation behavior represents a narrow interpretation that fails to account for the broader implications of undefined behavior in system stability and potential for exploitation. The fundamental issue lies in the violation of memory safety principles and the potential for cascading failures that could extend beyond simple denial of service into more serious security implications. The vulnerability demonstrates the importance of proper type handling and bounds checking in security-critical parsing operations, particularly those involving user-supplied data that must be processed without compromising system integrity.