# CVE-2026-101099: ag-ui Kotlin SDK exception handling flaw in SseParser

Source: https://junglewise.ai/threats/cve-2026-101099-a-vulnerability-was-detected-in-ag-ui-protocol-ag-ui-up-to-2026  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-28. Updated: 2026-09-28  
License: CC BY 4.0 with a link back

CVE-2026-101099 · Severity: medium · CVSS 4.3 · Published 2026-09-28

The ag-ui Kotlin SDK is vulnerable to improper exception handling when parsing JSON events from agent endpoints. A deeply nested JSON payload can trigger a StackOverflowError that bypasses the parser's exception handler, causing the application or Android process to terminate unexpectedly, disrupting service availability.

Vendors: [Ag-Ui-Protocol](https://junglewise.ai/threats/vendors/ag-ui-protocol).

## Quick answers

**Is CVE-2026-101099 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-101099 being exploited in the wild.

**How severe is CVE-2026-101099?** Medium severity, with a CVSS score of 4.3, published 28 September 2026.

**Which products and versions are affected?** Ag-Ui-Protocol ag-ui Kotlin SDK up to 2026-09-23.

**Is there a fix for CVE-2026-101099?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-101099 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-101099?** Check whether you run Ag-Ui-Protocol ag-ui Kotlin SDK 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.

## Technical details

The SseParser.kt component in ag-ui's Kotlin Community SDK uses kotlinx.serialization without a parse-depth limit, allowing deeply nested JSON to trigger StackOverflowError (an Error, not Exception) that escapes the catch(Exception) handler. This is a CWE-755 (improper exception handling) and CWE-400 (uncontrolled resource consumption) issue; a remote attacker controlling a malicious or compromised agent endpoint can craft input to cause process termination. The fix awaits acceptance in a pending pull request.

## Affected products

- ag-ui-protocol ag-ui Kotlin SDK up to 2026-09-23

## Timeline

- 2026-09-28: disclosed
- other: Pull request to fix awaits acceptance

## References

- [https://github.com/ag-ui-protocol/ag-ui/](https://github.com/ag-ui-protocol/ag-ui/)
- [https://github.com/ag-ui-protocol/ag-ui/issues/2442](https://github.com/ag-ui-protocol/ag-ui/issues/2442)