Log in Start free

Vulnerability · Published Sep 2, 2026 · Assigned by GitHub_M

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

Medium 5.9

In plain English

A medium-severity security flaw in httpx2 from pydantic. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 25% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.9Medium
Exploit odds (30 days)0.3%top 75.4% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Debian:14python-httpx22.12.0-1DEBIAN-CVE-2026-84378
PyPIhttpx22.10.0GHSA-f2fp-rgf2-35cp
PyPIhttpx22.10.0PYSEC-2026-3847
Ubuntu:26.10python-httpx2no fix listedUBUNTU-CVE-2026-84378

Affected products (as reported)

VendorProductVersions
pydantic httpx2 >= 2.5.0, < 2.10.0

Weakness: CWE-407 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

References