CVE-2026-96889 in Red Hat
Summary
by MITRE • 09/23/2026
A flaw was found in librsvg. When processing an SVG document containing nested XML inclusions (Xincludes) with duplicate entity declarations, a use-after-free error can occur. This vulnerability arises because the library incorrectly frees an XML entity that is still in use by the parser. An attacker could potentially exploit this to cause a denial of service or execute arbitrary code.
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Analysis
by VulDB Data Team • 09/23/2026
The vulnerability identified within librsvg represents a critical memory management flaw rooted in the handling of Extensible Markup Language (XML) inclusion mechanisms, specifically Xincludes, when combined with duplicate entity declarations. Librsvg is a widely used library for rendering Scalable Vector Graphics on Linux and other Unix-like systems, often integrated into desktop environments and web browsers to display vector images. The core technical flaw occurs during the parsing phase of an SVG document that contains nested XML inclusions. When such documents include multiple references to entities with identical names or structures, the internal parser logic fails to maintain proper reference counting for these XML entities. Specifically, the library incorrectly frees a memory block associated with an XML entity while it is still actively referenced by the ongoing parsing process. This results in a use-after-free condition, where the application attempts to access memory that has already been deallocated and potentially reused by other parts of the system or attacker-controlled data structures.
From a technical perspective, this flaw aligns closely with CWE-416, which describes Use After Free vulnerabilities. The root cause lies in the lifecycle management of XML entities within the parser's internal state machine. When an Xinclude is processed, the library loads external resources and integrates them into the document tree. If duplicate entity declarations are present, particularly in nested structures, the reference counting mechanism does not accurately track all active pointers to these entities. Consequently, one instance of the entity may be freed prematurely while another part of the parser still holds a valid pointer to it. This discrepancy creates an opportunity for memory corruption, as subsequent operations on the dangling pointer can lead to undefined behavior. The severity of this issue is amplified by the fact that SVG files are often processed from untrusted sources, such as web pages or email attachments, making them a frequent target for exploitation attempts.
The operational impact of exploiting this vulnerability is significant and multifaceted. In its most benign form, an attacker can trigger a denial of service by causing the application using librsvg to crash due to segmentation faults resulting from accessing invalid memory addresses. However, given the nature of use-after-free vulnerabilities in complex parsers like those handling XML and SVG, the potential for arbitrary code execution is substantial. By carefully crafting malicious SVG documents with specific sequences of Xincludes and entity declarations, an attacker can manipulate the heap layout to control what data overwrites the freed memory region. This allows for the hijacking of program flow or the injection of shellcode, leading to remote code execution on the victim's system. Such exploits are particularly dangerous in environments where librsvg is used within sandboxed contexts that may not have robust mitigations against heap exploitation techniques.
This vulnerability maps directly to several entries in the MITRE ATT&CK framework, reflecting its tactical utility for adversaries. It falls under the category of Initial Access via Valid Accounts or Trusted Relationships if delivered through phishing emails containing malicious SVG attachments, and it leverages Execution techniques involving command injection or dynamic library loading depending on how the memory corruption is exploited. Furthermore, it relates to Defense Evasion by bypassing application sandbox restrictions through heap-based exploitation methods that avoid triggering standard security checks. The presence of nested Xincludes serves as a specific vector for evading simple pattern-matching defenses that might not account for complex XML parsing edge cases involving duplicate entities.
Mitigation strategies must address both the immediate technical flaw and broader operational risks. For system administrators, applying vendor-provided patches to update librsvg is the primary remediation step. Since this vulnerability exists in the core parsing logic, relying on input validation alone at the application level is insufficient; the library itself must be updated to correct its reference counting mechanisms for XML entities during Xinclude processing. Developers integrating librsvg should ensure that their applications are configured to use the latest stable version of the library and consider implementing strict limits on SVG file size and complexity to reduce the attack surface. Additionally, enabling memory protection features such as Address Space Layout Randomization (ASLR) and Heap Canaries can help mitigate the impact of exploitation attempts by making it more difficult for attackers to predict memory layouts or overwrite critical control data. Regular security audits focusing on XML parsing libraries are recommended to identify similar issues in other components that handle complex document structures with nested includes and entity definitions.