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Fencer Vulns
medium 5.9

CVE-2026-84378 json

HTTPX2: Quadratic SSE line buffering can cause CPU denial of service

published 2026-09-02 2 mo ago modified 2026-09-10 1 mo ago also GHSA-f2fp-rgf2-35cp , PYSEC-2026-3847 , EUVD-2026-70242

cvss
5.9
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 24%
public exploits
0
none known

Summary

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.

Patch / fix

  • pypi httpx2 2.10.0
  • python-httpx2 Debian 14 2.12.0-1

debian advisories DEBIAN-CVE-2026-84378

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-84378 updated cvss 5.9

httpx2: HTTPX2: Denial of Service via crafted Server-Sent Events stream

  • Red Hat Lightspeed Core lightspeed-core/lightspeed-stack-rhel9 Red Hat OpenShift AI (RHOAI) rhoai/odh-automl-rhel9, rhoai/odh-vllm-gaudi-rhel9, rhoai/odh-kserve-autogluon-server-rhel9, rhoai/odh-kserve-storage-initializer-rhel9
    affected: workaround, no fix available “Fix deferred”
  • Red Hat AI Inference Server 3.5 rhaii/vllm-gaudi-rhel9 1791427182, rhaii/vllm-spyre-rhel9 1791818357
    fixed: vendor fix RHSA-2026:82061
  • Red Hat Migration Toolkit for Applications 8 mta/mta-solution-server-rhel9 Red Hat Enterprise Linux command line assistant rhel-cla/rhel-knowledge-bridge-rhel10
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
2 mo ago

Exploit prediction

0.32% chance of exploitation in the next 30 days, higher than 24% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
OSV 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
GitHub 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
pypi httpx2
>=2.5.0, <2.10.0
2.10.0

Affected products

  • pydantic httpx2

Classification

Weakness
  • CWE-407 Inefficient Algorithmic Complexity

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.