CVE-2026-110261 in ASM
Summary
by MITRE • 10/14/2026
OW2 ASM 3.0 before 9.11 contains a denial of service vulnerability that allows attackers to exhaust CPU by supplying crafted class files processed with ClassWriter.COMPUTE_FRAMES. Attackers can craft methods that make the unbounded MethodWriter.computeAllFrames() fix point algorithm converge slowly, tying up transforming threads for unbounded time.
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Analysis
by VulDB Data Team • 10/14/2026
The OW2 ASM library is a widely used Java bytecode manipulation and analysis framework that enables developers to generate, transform, or analyze existing classes dynamically at runtime. A critical security flaw exists in versions prior to 9.11 involving the ClassWriter class when configured with the COMPUTE_FRAMES flag. This vulnerability manifests as a denial of service condition where an attacker can exhaust system resources by supplying maliciously crafted Java class files for processing. The core technical issue lies within the internal implementation of MethodWriter.computeAllFrames, which is responsible for calculating stack map frames required for JVM verification when automatic frame computation is enabled.
The specific mechanism exploited involves the fix point algorithm used to compute these frames. When ASM processes a method with COMPUTE_FRAMES, it iteratively updates type information until no further changes occur, indicating convergence. An attacker can construct class files containing methods designed such that this iterative process converges extremely slowly or enters an effectively infinite loop due to subtle logical flaws in the frame calculation logic for certain complex control flow patterns. This causes the thread responsible for transforming or analyzing the bytecode to remain occupied for an unbounded amount of time, leading to resource exhaustion and service degradation for any application relying on ASM for dynamic class loading or transformation tasks such as those found in web frameworks, AOP proxies, or serialization libraries.
From a classification perspective, this vulnerability aligns with CWE-400 Uncontrolled Resource Consumption, specifically manifesting through algorithmic complexity that allows an attacker to force excessive CPU usage without requiring significant memory allocation. In the context of the MITRE ATT&CK framework, this behavior corresponds to T1496 Resource Hijacking, where attackers leverage compromised or vulnerable systems for computational purposes, although in this specific instance, the primary intent is denial of service rather than cryptomining or other resource hijacking activities. The impact extends beyond simple CPU spikes; it can lead to thread pool exhaustion in server environments, causing legitimate requests to time out and resulting in a complete outage of dependent services that utilize ASM for bytecode manipulation during request processing.
Mitigation strategies primarily involve upgrading the OW2 ASM library to version 9.11 or later, where this specific algorithmic flaw has been addressed by optimizing the frame computation logic to prevent unbounded execution times on malformed inputs. For organizations unable to immediately upgrade, implementing strict input validation and sandboxing mechanisms for any class files processed with COMPUTE_FRAMES can provide partial protection. Additionally, configuring thread pools with appropriate timeout limits and maximum queue sizes can mitigate the impact of such attacks by ensuring that a single malicious request does not monopolize processing resources indefinitely. Security teams should also monitor for unusual CPU spikes correlated with bytecode transformation activities as an indicator of potential exploitation attempts targeting this vulnerability in legacy systems still running older ASM versions.