# CVE-2026-120234: ag-ui HTTP Transport unbounded response buffering

Source: https://junglewise.ai/threats/cve-2026-120234-a-weakness-has-been-identified-in-ag-ui-protocol-ag-ui-up-to-0-0  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-01. Updated: 2026-11-01  
License: CC BY 4.0 with a link back

CVE-2026-120234 · Severity: medium · CVSS 4.3 · Published 2026-11-01

ag-ui is a JavaScript library that enables AI agents to interact with frontend applications. A flaw in its HTTP transport layer causes the client to read entire error response bodies into memory without limits. An attacker hosting a malicious endpoint can return a huge error response, exhausting the client's memory and crashing the application, while injecting misleading content into logs and error messages.

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

## Quick answers

**Is CVE-2026-120234 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-120234 being exploited in the wild.

**How severe is CVE-2026-120234?** Medium severity, with a CVSS score of 4.3, published 1 November 2026.

**Which products and versions are affected?** Ag-Ui-Protocol Ag-Ui up to 0.0.58.

**Is there a fix for CVE-2026-120234?** No fixed version is recorded yet. Read error response bodies through a streaming reader under a strict byte budget (e.g. truncate after 8 KB); construct error messages from status code and a bounded excerpt only, never the full body. 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-2026-120234 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-120234?** Check whether you run Ag-Ui-Protocol Ag-Ui 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


Read error response bodies through a streaming reader under a strict byte budget (e.g. truncate after 8 KB); construct error messages from status code and a bounded excerpt only, never the full body.

## Technical details

The vulnerability is an unbounded resource allocation in the HTTP error path of @ag-ui/client's runHttpRequest function. When a non-2xx response is received, the code calls e.text() on the response body with no size cap or streaming, then constructs an Error object that embeds and duplicates the full body. A remote attacker controlling a server endpoint can send a 500 status with a multi-gigabyte text payload, causing out-of-memory conditions on the client side. CWE-400 / CWE-770.

## Affected products

- ag-ui-protocol ag-ui up to 0.0.58

## Timeline

- 2026-08-25: disclosed: Issue #2521 opened on GitHub by ez-lbz
- 2026-11-01: advisory

## 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/2521](https://github.com/ag-ui-protocol/ag-ui/issues/2521)

## Related threats

- [ag-ui-protocol ag-ui resource exhaustion in interrupt expiry](https://junglewise.ai/threats/cve-2026-120237-a-flaw-has-been-found-in-ag-ui-protocol-ag-ui-up-to-0-0-58)
- [ag-ui Transport Decoder Handler improper input validation](https://junglewise.ai/threats/cve-2026-120236-a-vulnerability-was-detected-in-ag-ui-protocol-ag-ui-up-to-0-0)
- [ag-ui SSE parser resource exhaustion](https://junglewise.ai/threats/cve-2026-120235-a-security-vulnerability-has-been-detected-in-ag-ui-protocol-ag)
- [ag-ui HttpAgent credential and request body forwarding via redirect](https://junglewise.ai/threats/cve-2026-120233-a-security-flaw-has-been-discovered-in-ag-ui-protocol-ag-ui-up)
- [ag-ui JSON.parse uncaught exception in middleware](https://junglewise.ai/threats/cve-2026-101101-a-vulnerability-has-been-found-in-ag-ui-protocol-ag-ui-up-to)