What’s Vulnerable › Vulnerabilities

CVE-2026-88975: Http4s: Ember HTTP/2 buffers a frame's declared payload before checking SETTINGS_MAX_FRAME_SIZE

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-15 · updated 2026-09-16
• Weakness: CWE-400

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.

Affected products

• http4s: before 0.23.37; from 1.0.0-M1, < 1.0.0-M48

References

• 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
• https://github.com/http4s/http4s/security/advisories/GHSA-gq9p-f254-h286

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