CVE-2026-84378
HTTPX2: Quadratic SSE line buffering can cause CPU denial of service
- Published
- Updated
- Reserved
- Assigned by
- GitHub_M
Description
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.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_MCNA (assigner) | 3.1 | Medium5.9 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H |
| NVDNVD · Awaiting Analysis | 3.1 | Medium5.9 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H |
- EPSS (exploitation in 30 days)
- 0.32% · top 75% of all CVEs (6 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: no · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 5.9.
Weakness
Affected products
Affected packages
From reviewed advisories of the GitHub Advisory Database.
- PyPIhttpx2GHSA-f2fp-rgf2-35cp (opens in a new tab)
References (5)
- https://github.com/pydantic/httpx2/security/advisories/GHSA-f2fp-rgf2-35cp (opens in a new tab)x_refsource_CONFIRM
- https://github.com/pydantic/httpx2/pull/1071 (opens in a new tab)x_refsource_MISC
- https://github.com/pydantic/httpx2/pull/1117 (opens in a new tab)x_refsource_MISC
- https://github.com/pydantic/httpx2/commit/cbfc0e04ef6507da29ccbb3b9c2e5b23dd693414 (opens in a new tab)x_refsource_MISC
- https://github.com/pydantic/httpx2/releases/tag/v2.10.0 (opens in a new tab)x_refsource_MISC
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisory GHSA-f2fp-rgf2-35cp (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://trackcve.app/cve/CVE-2026-84378)Record last updated .