Bug 2527694 (CVE-2026-84378)

Summary:	CVE-2026-84378 httpx2: HTTPX2: Denial of Service via crafted Server-Sent Events stream
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security <prodsec-ir-bot>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	ebourniv, gbenhaim, hasun, kaycoth, niyer, nyancey, ptisnovs, sbunciak, twaugh
Target Milestone:	---	Keywords:	Security
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Hardware:	All
OS:	Linux
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Doc Text:	A flaw was found in httpx2, a Python HTTP client. The Server-Sent Events (SSE) parser in httpx2 can be exploited by a remote attacker. By sending a specially crafted stream where an unterminated line is split across many response chunks, the parser repeatedly copies and rescans buffered text. This quadratic processing work consumes excessive CPU resources, leading to a Denial of Service (DoS) by blocking synchronous workers or asynchronous event loops.	Story Points:	---
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oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-09-02 18:10:51 UTC

HTTPX2 is a next generation HTTP client for Python. From 2.5.0 until 2.10.0, the HTTPX2 Server-Sent Events parser in src/httpx2/httpx2/_sse.py repeatedly copies and rescans buffered text in _SSELineDecoder.decode() when an attacker-controlled or compromised SSE endpoint splits one unterminated line across many response chunks. The behavior affects httpx2.Client.sse() and httpx2.AsyncClient.sse(), and the total processing work grows quadratically with the line length, allowing a crafted stream to consume excessive CPU and block a synchronous worker or asynchronous event loop. This issue is fixed in version 2.10.0.