CVE-2021-42756

CRITICALNVD 9.89.8—
EchelonGraph scoreMEDIUM confidence

Score 9.8 from GitHub Security Advisory (severity: CRITICAL) published 2023-02-16. NVD baseline CVSS 9.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
Elevated
9.8
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 35%CVSS: 9.8Exploit: NoneExposed: 0

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

Multiple stack-based buffer overflow vulnerabilities [CWE-121] in the proxy daemon of FortiWeb 5.x all versions, 6.0.7 and below, 6.1.2 and below, 6.2.6 and below, 6.3.16 and below, 6.4 all versions may allow an unauthenticated remote attacker to achieve arbitrary code execution via specifically crafted HTTP requests.

CVSS v3
9.8
EG Score
9.8(medium)
EG Risk
75(Track)
EG Risk 75/100SSVC: 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
Severity98% × 45%
Exploitation40% × 40%
Automatability100% × 15%
Action: Routine — remediate on your standard cadence.
EPSS
98.3%
KEV
Not listed

Published

February 16, 2023

Last Modified

November 21, 2024

Advisory Details (1)

Auto-updated Jun 9, 2026
No patch confirmed yet.
generic

PSIRT | FortiGuard Labs

https://fortiguard.com/psirt/FG-IR-21-186

Weakness Classification(2)

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

Data Freshness Timeline

(refreshed 9× in last 7d / 38× 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. 2026-07-23 14:16 UTCEPSS rescore
  2. 2026-07-23 02:04 UTCEG score recompute
  3. 2026-07-22 22:51 UTCEG score recompute
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  44. 2026-05-31 22:29 UTCEPSS rescore
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  53. 2026-05-26 07:17 UTCEPSS rescore
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  55. 2026-05-26 07:17 UTCEPSS rescore
  56. 2026-05-25 06:37 UTCEG score recompute
  57. 2026-05-25 06:37 UTCGHSA enrichment

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Frequently asked(5)

What is CVE-2021-42756?
CVE-2021-42756 is a critical vulnerability published on February 16, 2023. Multiple stack-based buffer overflow vulnerabilities [CWE-121] in the proxy daemon of FortiWeb 5.x all versions, 6.0.7 and below, 6.1.2 and below, 6.2.6 and below, 6.3.16 and below, 6.4 all versions may allow an unauthenticated remote attacker to achieve arbitrary code execution via specifically…
When was CVE-2021-42756 disclosed?
CVE-2021-42756 was first published in the National Vulnerability Database on February 16, 2023, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-42756 actively exploited?
CVE-2021-42756 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 98.3% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-42756?
CVE-2021-42756 has a CVSS v3 base score of 9.8 (NVD).
How do I remediate CVE-2021-42756?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-42756, 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

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