CVE-2025-6499 in libucl
Summary
by MITRE • 06/23/2025
A vulnerability classified as problematic was found in vstakhov libucl up to 0.9.2. Affected by this vulnerability is the function ucl_parse_multiline_string of the file src/ucl_parser.c. The manipulation leads to heap-based buffer overflow. The attack needs to be approached locally. The exploit has been disclosed to the public and may be used.
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Analysis
by VulDB Data Team • 06/23/2025
The vulnerability identified as CVE-2025-6499 represents a critical heap-based buffer overflow within the vstakhov libucl library version 0.9.2 and earlier. This issue resides in the ucl_parse_multiline_string function located within the src/ucl_parser.c file, making it a significant concern for systems that rely on this universal configuration library for parsing various data formats including json yaml and other structured text configurations. The library is widely used in server applications and network infrastructure tools where configuration parsing is essential for system operation.
The technical flaw manifests when the ucl_parse_multiline_string function processes malformed input data that exceeds allocated buffer boundaries, leading to memory corruption that can be exploited through heap-based buffer overflow techniques. This vulnerability specifically affects the parser's handling of multiline string data structures where insufficient bounds checking occurs during memory allocation and data copying operations. The flaw allows an attacker to write beyond the allocated memory space, potentially corrupting adjacent memory locations and creating opportunities for arbitrary code execution or system instability.
The operational impact of this vulnerability extends beyond simple memory corruption as it enables local privilege escalation and denial of service conditions within applications that utilize libucl for configuration parsing. Systems running services that parse user-provided configuration files or data streams become vulnerable to exploitation, particularly those that process untrusted input from network sources or local users. The disclosed exploit demonstrates that attackers can leverage this vulnerability to execute malicious code with the privileges of the affected application, potentially leading to complete system compromise or unauthorized access to sensitive data.
Security professionals should note that this vulnerability aligns with CWE-121 heap-based buffer overflow weakness and represents a direct threat to software supply chain integrity given libucl's widespread adoption in enterprise and open source applications. The ATT&CK framework categorizes this as a memory corruption technique that could be leveraged for privilege escalation and persistence mechanisms. Organizations utilizing libucl in their infrastructure should immediately implement mitigations including input validation, memory protection mechanisms, and application sandboxing to reduce the attack surface. The recommended remediation involves upgrading to version 0.9.3 or later where the buffer overflow has been patched through proper bounds checking and memory management improvements. Additionally, deploying runtime protections such as address space layout randomization and stack canaries can provide additional defense in depth measures against exploitation attempts.