CVE-2026-112046 in ASM
Summary
by MITRE • 10/18/2026
OW2 ASM 9.11 before 9.11.1 contains an infinite loop vulnerability in Label.resolve() caused by 16-bit forward-reference offsets truncating when rewritten methods exceed 64 KB. Attackers can supply crafted class files whose transformed code grows past 65535 bytes, hanging ClassReader.accept() and denying service to build tools, instrumenters, agents, or analyzers.
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Analysis
by VulDB Data Team • 10/18/2026
The vulnerability identified in OW2 ASM versions prior to 9.11.1 represents a critical reliability flaw within the core bytecode manipulation library used extensively across the Java ecosystem. This issue specifically manifests during the processing of class files where method bodies are transformed and subsequently rewritten by tools such as build systems, runtime instrumenters, or static analyzers. The root cause lies in the Label.resolve() function, which is responsible for resolving jump targets within bytecode instructions. When a modified method exceeds 64 kilobytes in size, the internal handling of forward-reference offsets suffers from integer truncation due to reliance on 16-bit signed values without adequate bounds checking or expansion logic. This architectural limitation means that any offset calculation resulting in a value larger than what can be represented by a short integer will wrap around, leading to incorrect label resolution and subsequent control flow errors during the rewriting process.
From an operational perspective, this flaw results in a denial of service condition rather than arbitrary code execution or data leakage. Attackers who possess the ability to supply crafted class files to systems utilizing vulnerable versions of ASM can trigger infinite loops within the ClassReader.accept() method. Because the label resolution logic enters a state where it cannot correctly map instruction pointers due to the truncated offsets, the parsing engine fails to terminate its traversal of the bytecode structure. This effectively hangs the processing thread indefinitely, causing build tools like Maven or Gradle to freeze during compilation phases, runtime agents such as Java Agents used for monitoring or security scanning to become unresponsive, and static analysis platforms to stall when ingesting large classes. The impact is particularly severe in continuous integration environments where automated builds are expected to complete within strict time limits, potentially blocking deployment pipelines and disrupting development workflows.
This vulnerability aligns with CWE-835, which describes the use of a loop with an untimely or missing termination condition, specifically arising from improper handling of data types leading to infinite iteration. Furthermore, it can be mapped to MITRE ATT&CK technique T1496, Resource Hijacking, as the exploitation results in the consumption of computational resources and time without achieving further malicious objectives beyond disruption. The lack of proper validation for method size relative to offset limits highlights a gap in defensive programming practices within library code that assumes typical class sizes remain within standard bounds.
Mitigation strategies primarily involve upgrading to OW2 ASM version 9.11.1 or later, where the developers have addressed this truncation issue by implementing appropriate handling for large methods and ensuring that label resolution logic accounts for offsets beyond the 64 KB threshold. Organizations relying on bytecode manipulation libraries should audit their dependency trees to ensure no legacy versions are present in production environments. Additionally, defensive coding practices within applications using ASM can include setting timeouts on parsing operations or validating class file sizes before initiating complex transformations, although these measures serve as secondary safeguards rather than primary fixes for the underlying library defect.