CVE-2026-1757 in libxml2
Summary
by MITRE • 02/02/2026
A flaw was identified in the interactive shell of the xmllint utility, part of the libxml2 project, where memory allocated for user input is not properly released under certain conditions. When a user submits input consisting only of whitespace, the program skips command execution but fails to free the allocated buffer. Repeating this action causes memory to continuously accumulate. Over time, this can exhaust system memory and terminate the xmllint process, creating a denial-of-service condition on the local system.
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Analysis
by VulDB Data Team • 03/12/2026
The vulnerability described in CVE-2026-1757 represents a classic memory management flaw within the xmllint utility that forms part of the widely-used libxml2 library. This interactive shell implementation demonstrates a critical oversight in resource handling where allocated memory buffers fail to be properly deallocated during specific input processing scenarios. The flaw manifests when users provide input consisting exclusively of whitespace characters, which triggers a code path that bypasses normal command execution while leaving memory allocation untouched. This particular condition creates a persistent memory leak that accumulates with each repeated occurrence, fundamentally undermining the application's resource management capabilities.
The technical implementation of this vulnerability stems from improper memory deallocation logic within the xmllint shell's input processing routine. When whitespace-only input is received, the utility correctly identifies that no meaningful command execution should occur, yet it fails to execute the necessary cleanup procedures that would normally occur after command processing. This creates a state where memory allocated for storing the input buffer remains allocated indefinitely, with each subsequent whitespace input adding to the growing memory footprint. The flaw operates at the level of the shell's command loop where input parsing and buffer management intersect, making it particularly insidious as it can be triggered through normal user interaction patterns.
From an operational perspective, this vulnerability creates a significant denial-of-service condition that can be easily exploited by malicious actors or inadvertently triggered by users. The memory consumption grows incrementally with each whitespace input, eventually leading to system resource exhaustion that terminates the xmllint process. This condition affects local system availability and can potentially impact systems that rely on xmllint for XML processing tasks, particularly in environments where automated or continuous processing occurs. The vulnerability's exploitation requires minimal effort, as it only necessitates repeated input of whitespace characters, making it particularly dangerous in automated or unattended environments.
The vulnerability aligns with CWE-401, which specifically addresses improper release of memory, and demonstrates characteristics consistent with the ATT&CK technique T1499.1 for network denial-of-service attacks. The memory leak pattern suggests a failure in the application's resource lifecycle management, where allocated memory is not properly tracked and released. This flaw represents a fundamental breakdown in defensive programming practices, as proper memory management should account for all code paths, including those that bypass normal execution flows. The vulnerability's impact extends beyond simple resource consumption, as it can potentially be leveraged to cause system instability or resource exhaustion in environments where xmllint is frequently used or integrated into automated workflows.
Mitigation strategies for CVE-2026-1757 should focus on implementing proper memory management practices within the xmllint shell implementation. The most effective approach involves ensuring that all allocated buffers are properly freed regardless of the input processing path taken. This requires code modifications to guarantee that memory cleanup routines execute consistently across all input conditions, particularly those that skip command execution. System administrators should also consider implementing monitoring mechanisms to detect unusual memory consumption patterns in processes that utilize xmllint. Additionally, users should be advised to avoid repetitive whitespace input patterns and to regularly monitor system resources when using xmllint in production environments, while applying patches or updates to libxml2 as soon as they become available to address the underlying memory management flaw.