# CVE-2026-110259: OW2 ASM uncontrolled recursion in ClassWriter

Source: https://junglewise.ai/threats/cve-2026-110259-ow2-asm-3-0-before-9-11-contains-an-uncontrolled-recursion  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-14. Updated: 2026-10-26  
License: CC BY 4.0 with a link back

CVE-2026-110259 · Severity: medium · CVSS 5.5 · Published 2026-10-14

OW2 ASM is a Java bytecode manipulation library used by frameworks and tools to analyze and generate Java classes. A flaw in versions before 9.11 allows attackers to craft malicious class files that trigger unbounded recursion in the ClassWriter component, causing the application to crash with a StackOverflowError. This leads to denial of service against any system processing untrusted Java bytecode.

Technologies: [OW2 ASM](https://junglewise.ai/threats/technologies/asm). Vendors: [OW2](https://junglewise.ai/threats/vendors/ow2).

## Quick answers

**Is CVE-2026-110259 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-110259 being exploited in the wild.

**How severe is CVE-2026-110259?** Medium severity, with a CVSS score of 5.5, published 14 October 2026.

**Which products and versions are affected?** OW2 ASM 3.0 before 9.11.

**Is there a fix for CVE-2026-110259?** Yes: fixed in ASM 9.11. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-110259 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-110259?** Check whether you run OW2 ASM at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in ASM 9.11

## Technical details

The vulnerability is an uncontrolled recursion flaw in the ClassWriter.replaceAsmInstructions() method when processing forward jumps in large methods. An attacker can supply a specially crafted class file with many long forward jumps that trigger unbounded recursion in the toByteArray() method, resulting in a StackOverflowError. The flaw was fixed in version 9.11 with commit !459, which redesigned the bytecode storage mechanism to avoid recursion.

## Affected products

- OW2 ASM 3.0 before 9.11

## Timeline

- 2026-10-14: advisory

## References

- [https://repo1.maven.org/maven2/](https://repo1.maven.org/maven2/)
- [https://asm.ow2.io/versions.html](https://asm.ow2.io/versions.html)

## Related threats

- [OW2 ASM infinite loop in Label.resolve with large methods](https://junglewise.ai/threats/cve-2026-112046-ow2-asm-9-11-before-9-11-1-contains-an-infinite-loop)
- [OW2 ASM excessive resource consumption in Analyzer.analyze()](https://junglewise.ai/threats/cve-2026-110591-ow2-asm-1-4-3-before-9-11-contains-an-excessive-resource)
- [OW2 ASM uncontrolled memory allocation in JSRInlinerAdapter](https://junglewise.ai/threats/cve-2026-110270-ow2-asm-3-0-before-9-11-contains-an-uncontrolled-memory)
- [OW2 ASM quadratic memory allocation in MethodWriter](https://junglewise.ai/threats/cve-2026-110260-ow2-asm-3-0-before-9-11-contains-a-quadratic-memory-allocation)