Pydantic Httpx2 up to 2.9.x Server-Sent Events Parser _sse.py _SSELineDecoder.decode information exposure through microarchitectural state after transient execution

Summaryinfo

A vulnerability, which was classified as problematic, was found in Pydantic Httpx2 up to 2.9.x. This affects the function _SSELineDecoder.decode of the file src/httpx2/httpx2/_sse.py of the component Server-Sent Events Parser. The manipulation results in information exposure through microarchitectural state after transient execution. This vulnerability is cataloged as CVE-2026-84378. The attack may be launched remotely. There is no exploit available.

Detailsinfo

A vulnerability was found in Pydantic Httpx2 up to 2.9.x. It has been classified as problematic. Affected is the function _SSELineDecoder.decode of the file src/httpx2/httpx2/_sse.py of the component Server-Sent Events Parser. The manipulation with an unknown input leads to a information exposure through microarchitectural state after transient execution vulnerability. CWE is classifying the issue as CWE-1342. The processor does not properly clear microarchitectural state after incorrect microcode assists or speculative execution, resulting in transient execution. This is going to have an impact on availability. CVE summarizes:

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.

The advisory is available at github.com. This vulnerability is traded as CVE-2026-84378 since 09/01/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. Technical details are known, but there is no available exploit. This vulnerability is assigned to T1592.001 by the MITRE ATT&CK project.

Upgrading to version 2.10.0 eliminates this vulnerability.

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Productinfo

Vendor

• Pydantic

Name

• Httpx2

Version

• 2.0
• 2.1
• 2.2
• 2.3
• 2.4
• 2.5
• 2.6
• 2.7
• 2.8
• 2.9

Website

• Product: https://github.com/pydantic/httpx2/

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CPE 2.2info

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