Medium 5.9Published Sep 2, 2026

CVE-2026-84378HTTPX2: Quadratic SSE line buffering can cause CPU denial of service

Updated under an hour ago (2026-10-19 06:25 UTC)

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It affects pydantic httpx2. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

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Every CVE for pydantic httpx2

Exploited in the last 30 days

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.

CVSS: 5.9 MEDIUM (v3.1, CNA)CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness (CWE): CWE-407
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Awaiting Analysis
Record last updated: Sep 2, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

pydantic httpx2 pydantic:httpx2 (from the name)	from 2.5.0, < 2.10.0	CNA record

References

https://github.com/pydantic/httpx2/security/advisories/GHSA-f2fp-rgf2-35cpx-refsource-confirm
https://github.com/pydantic/httpx2/pull/1071x-refsource-misc
https://github.com/pydantic/httpx2/pull/1117x-refsource-misc
https://github.com/pydantic/httpx2/commit/cbfc0e04ef6507da29ccbb3b9c2e5b23dd693414x-refsource-misc
https://github.com/pydantic/httpx2/releases/tag/v2.10.0x-refsource-misc

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.