HTTPX2: Quadratic SSE line buffering can cause CPU denial of service
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- High
- Impact type
- Denial of service
- Confidentiality · integrity · availability
- None · None · High
- Fix status
- Partial Red Hat: 1 fixed, 2 without a fix
Attack profile from CVSS 3.1 · CNA. Fix status from CNA, GitHub and Red Hat. Impact type from CWE-407.
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.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| pydantic | httpx2 | 2.5.0 to before 2.10.0 | 2.10.0 | Patch available | CNA |
| — | httpx2 (PyPI) | 2.5.0 to before 2.10.0 | 2.10.0 | Patch available | GHSA-f2fp-rgf2-35cp |
- httpx2 Vendorpydantic Affected 2.5.0 to before 2.10.0 Fixed in 2.10.0 Patch available CNA
- httpx2 (PyPI) Vendor— Affected 2.5.0 to before 2.10.0 Fixed in 2.10.0 Patch available GHSA-f2fp-rgf2-35cp
Remediation
- Fix · CNA httpx2 (pydantic) Fixed in 2.10.0
- Fix · GHSA-f2fp-rgf2-35cp httpx2 (PyPI) Fixed in 2.10.0 Advisory →
Red Hat 2 advisories
- RHSA-2026:82371 Released 2026-10-13 · Red Hat rating CriticalRed Hat AI Inference 3.5.2 (spyre)
- Red Hat AI Inference Server 3.5 registry.redhat.io/rhaii/vllm-spyre-rhel9
- RHSA-2026:82061 Released 2026-10-13 · Red Hat rating CriticalRed Hat AI Inference Tech Preview 3.5.2 (Gaudi)
- Red Hat AI Inference Server 3.5 registry.redhat.io/rhaii/vllm-gaudi-rhel9
Vendor assessments
Red Hat
Red Hat rating: Moderate. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Lightspeed Core | Affected | No fix yet: Fix deferred |
| Red Hat OpenShift AI (RHOAI) | Affected | No fix yet: Fix deferred |
| Red Hat AI Inference Server 3.5 | Fixed | RHSA-2026:82061, RHSA-2026:82371 |
Not affected: 2 products
- Migration Toolkit for Applications 8
- Red Hat Enterprise Linux command line assistant
Timeline
- 2026-10-02 Threatist record created from CVE-2026-84378
- 2026-10-03 Alias added: GHSA-f2fp-rgf2-35cp
- 2026-10-13 Fix available: RHSA-2026:82061 · Red Hat
- 2026-10-13 Fix available: Red Hat AI Inference Server 3.5 · Red Hat
- 2026-10-14 Fix available: RHSA-2026:82371 · Red Hat
- 2026-10-15 Affected versions changed · Red Hat
References
Other 6
- https://github.com/pydantic/httpx2/security/advisories/GHSA-f2fp-rgf2-35cp
- https://github.com/pydantic/httpx2/pull/1071
- https://github.com/pydantic/httpx2/pull/1117
- https://github.com/pydantic/httpx2/commit/cbfc0e04ef6507da29ccbb3b9c2e5b23dd693414
- https://github.com/pydantic/httpx2/releases/tag/v2.10.0
- https://github.com/pydantic/httpx2
More pydantic vulnerabilities
- TI-2024-03518 Regular expression denial of service in Pydantic < 2.4.0 CVSS 3.1HIGH 7.5
- TI-2026-57990 HTTPX2: Multipart part header injection via unvalidated file Content-Type and custom headers CVSS 3.1MEDIUM 5.3
- TI-2026-41916 Path traversal in pydantic-settings CVSS 3.1MEDIUM 5.3
- TI-2026-20687 Pydantic AI Affected by Server-Side Request Forgery (SSRF) in URL Download Handling CVSS 3.1HIGH 8.6
- TI-2026-57993 HTTPX2: Streaming response decompression does not bound peak memory (decompression amplification) CVSS 3.1HIGH 7.5
- TI-2026-69551 Pydantic AI keeps concurrency slots after streams end early CVSS 3.1HIGH 7.5
Sources
- CVE-2026-84378 · CVE Program
- CVE-2026-84378 · NVD
- FIRST EPSS
- GHSA-f2fp-rgf2-35cp · GitHub Advisory Database · CC BY 4.0
- CVE-2026-84378 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences