CVE-2015-7557 in librsvg
Summary
by MITRE
The _rsvg_node_poly_build_path function in rsvg-shapes.c in librsvg before 2.40.7 allows context-dependent attackers to cause a denial of service (out-of-bounds heap read) via an odd number of elements in a coordinate pair in an SVG document.
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Analysis
by VulDB Data Team • 08/21/2022
The vulnerability identified as CVE-2015-7557 affects the librsvg library version 2.40.7 and earlier, specifically within the _rsvg_node_poly_build_path function located in rsvg-shapes.c. This flaw represents a classic buffer over-read condition that occurs when processing SVG (Scalable Vector Graphics) documents containing malformed coordinate data. The issue arises from insufficient input validation when handling polygonal elements that contain an odd number of coordinate pairs, creating a scenario where the parsing logic attempts to access memory beyond the allocated bounds.
The technical implementation of this vulnerability stems from the library's handling of SVG polygonal shapes where coordinate pairs are expected to follow a consistent format of x,y values. When an odd number of elements is present in a coordinate sequence, the parsing algorithm fails to properly validate the data structure, leading to a heap-based out-of-bounds read operation. This memory access violation occurs during the path building phase of SVG rendering, specifically when the library attempts to process polygon vertices. The flaw manifests as a context-dependent vulnerability, meaning it only triggers under specific conditions related to the structure of the SVG document being processed, making it particularly challenging to detect during routine security assessments.
The operational impact of this vulnerability extends beyond simple denial of service, as it can potentially be exploited to cause application crashes or system instability when processing maliciously crafted SVG files. Attackers can leverage this weakness by embedding specially constructed SVG documents with malformed coordinate data into web pages, email attachments, or other vectorized content. The out-of-bounds heap read can result in unpredictable behavior including segmentation faults, memory corruption, or even potential information disclosure depending on the specific memory layout and system configuration. This vulnerability directly aligns with CWE-125, which describes out-of-bounds read conditions, and can be classified under ATT&CK technique T1203, representing exploitation of software vulnerabilities for denial of service or system instability.
Mitigation strategies for CVE-2015-7557 primarily involve updating to librsvg version 2.40.7 or later, where the vulnerability has been addressed through improved input validation and bounds checking mechanisms. System administrators should implement comprehensive patch management procedures to ensure all affected systems receive the necessary updates promptly. Additionally, organizations can deploy defensive measures such as SVG validation filters and content sanitization processes to prevent malformed SVG content from reaching vulnerable applications. Network-based protections can include web application firewalls that inspect and filter SVG content, while application-level protections should enforce strict input validation and implement proper error handling for malformed data. The fix implemented in the patched version typically involves enhancing the coordinate parsing logic to properly validate the number of elements in coordinate pairs and ensure that all memory accesses remain within valid bounds, thereby preventing the out-of-bounds heap read condition that previously enabled the denial of service attack vector.