CVE-2026-88975

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

Published Sep 15, 2026 CVSS 3.1 · 7.5 High EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Github GHSA Github GHSA GHSA-gq9p-f254-h286 Http4s: Ember HTTP/2 buffers a frame's declared payload before checking SETTINGS_MAX_FRAME_SIZE
History
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Http4s
Http4s http4s
Vendors & Products Http4s
Http4s http4s
Type Values Removed Values Added
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.
Title Http4s: Ember HTTP/2 buffers a frame's declared payload before checking SETTINGS_MAX_FRAME_SIZE
Weaknesses CWE-400
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
GitHub_M
Published
Updated
Sep 16, 2026, 2:43 PM
Reserved
Sep 10, 2026, 4:02 PM
Status
Deferred
Published
Sep 15, 2026, 8:19 PM
Modified
Sep 16, 2026, 8:39 PM