CVE-2026-84378

MEDIUMPre-NVD 5.95.9—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 5.9 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.3%, top 75% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, secondary
5.9EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 5.9Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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 v3
5.9
EG Score
5.9(medium)
EG Risk
27(Track)
EG Risk 27/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity59% × 45%
Exploitation0% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
25%
KEV
Not listed

Published

September 2, 2026

Last Modified

September 9, 2026

Advisory Details (5)

Auto-updated Sep 2, 2026
Patch available. Sources: github_commit, github_release, github, github_pr.
github_release Patch Available

v2.10.0

Patch available: pydantic/httpx2 v2.10.0

https://github.com/pydantic/httpx2/releases/tag/v2.10.0
github_commit Patch Available

commit cbfc0e04ef65 (pydantic/httpx2)

Patch available: pydantic/httpx2 v2.10.0 (contains commit cbfc0e04ef65)

https://github.com/pydantic/httpx2/commit/cbfc0e04ef6507da29ccbb3b9c2e5b23dd693414
github_pr Patch Available

Improve SSE chunk buffering performance

Patch available: pydantic/httpx2 v2.10.0 (PR #1117 merged 2026-08-06)

https://github.com/pydantic/httpx2/pull/1117
github_pr Patch Available

Add `max_event_size` to cap SSE event buffering

Patch available: pydantic/httpx2 v2.10.0 (PR #1071 merged 2026-08-05)

https://github.com/pydantic/httpx2/pull/1071
github Patch Available

Quadratic SSE line buffering can cause CPU denial of service · Advisory · pydantic/httpx2 · GitHub

https://github.com/pydantic/httpx2/security/advisories/GHSA-f2fp-rgf2-35cp

Vendor Advisories for CVE-2026-84378(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Affected Packages

(2 across 2 ecosystems)
Debian:14(1)
PackageVulnerable rangeFixed inDependents
python-httpx22.4.0-1, 2.5.0-12.12.0-1—
PyPI(1)
PackageVulnerable rangeFixed inDependents
httpx22.5.0 ... 2.9.1 (6 versions)2.10.0—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 12× in last 7d / 30× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-09-18 19:28 UTCEPSS rescore
  2. 2026-09-18 10:01 UTCEG score recompute
  3. 2026-09-17 19:32 UTCEPSS rescore
  4. 2026-09-17 08:26 UTCEG score recompute
  5. 2026-09-16 14:09 UTCEPSS rescore
  6. 2026-09-16 06:50 UTCEG score recompute
  7. 2026-09-16 05:15 UTCEPSS rescore
  8. 2026-09-15 05:16 UTCEG score recompute
  9. 2026-09-15 03:12 UTCEPSS rescore
  10. 2026-09-15 03:12 UTCEPSS rescore
  11. 2026-09-14 03:32 UTCEG score recompute
  12. 2026-09-13 01:57 UTCEG score recompute
  13. 2026-09-12 00:21 UTCEG score recompute
  14. 2026-09-11 14:53 UTCEPSS rescore
  15. 2026-09-11 14:53 UTCEPSS rescore
  16. 2026-09-10 22:46 UTCEG score recompute
  17. 2026-09-09 05:52 UTCEG score recompute
  18. 2026-09-08 22:01 UTCEPSS rescore
  19. 2026-09-08 04:17 UTCEG score recompute
  20. 2026-09-07 02:42 UTCEG score recompute
  21. 2026-09-06 13:48 UTCEPSS rescore
  22. 2026-09-06 01:06 UTCEG score recompute
  23. 2026-09-05 15:31 UTCEPSS rescore
  24. 2026-09-04 23:26 UTCEG score recompute
  25. 2026-09-04 05:07 UTCEPSS rescore
Show 5 more
  1. 2026-09-02 19:31 UTCEG score recompute
  2. 2026-09-02 19:12 UTCEG score recompute
  3. 2026-09-02 18:36 UTCEG score recompute
  4. 2026-09-02 18:03 UTCEG score recompute
  5. 2026-09-02 18:01 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-84378?
CVE-2026-84378 is a medium vulnerability published on September 2, 2026. 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…
When was CVE-2026-84378 disclosed?
CVE-2026-84378 was first published in the National Vulnerability Database on September 2, 2026, with the most recent update on September 9, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-84378 actively exploited?
CVE-2026-84378 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 74.9% of all scored CVEs.
What is the CVSS score of CVE-2026-84378?
CVE-2026-84378 has a CVSS v3 base score of 5.9 (NVD).
How do I remediate CVE-2026-84378?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-84378, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-84378

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