# CVE-2021-33766: Microsoft Exchange Server Information Disclosure

- Exploited (CISA KEV): yes, added 2022-01-18
- Published: 2021-07-14
- CVSS: 7.3 HIGH (v3.1)
- EPSS: 98.2% (100th percentile)
- CWE: CWE-287

Microsoft Exchange Server Information Disclosure Vulnerability

## Edge WAF coverage (claimed by vendors, not measured)

| Vendor | Status | First rule | Days after publication |
|---|---|---|---|
| Cloudflare | Before feed history | — | — |
| AWS | No public claim | — | — |
| Microsoft Azure | No public claim | — | — |
| Google Cloud | Before feed history | — | — |
| Fastly | Before feed history | — | — |
| F5 | Rule published | 2023-08-08 | — |
| Akamai | No public source | — | — |
| OWASP CRS | Before feed history | — | — |

### F5

- 2023-08-08 · updated · rule 200013039
  > Updated: signature 200013039 "Microsoft Exchange ProxyToken authentication bypass" (Authentication/Authorization Attacks, risk High), systems: Outlook Web Access. References: CVE-2021-33766.
  Source: https://docs.cloud.f5.com/docs-v2/platform/changelogs/security-details-changelog
- 2023-09-12 · updated · rule 200013039
  > Updated: signature 200013039 "Microsoft Exchange ProxyToken authentication bypass" (Authentication/Authorization Attacks, risk High), systems: Outlook Web Access. References: CVE-2021-33766.
  Source: https://docs.cloud.f5.com/docs-v2/platform/changelogs/security-details-changelog

## Our test (measured)

- OWASP Core Rule Set 4.25.0, paranoia level 1, anomaly threshold 5, default CRS settings: passed (0 of 1 requests blocked), template CVE-2021-33766, 2026-11-02
- OWASP Core Rule Set 4.25.0, paranoia level 2, anomaly threshold 5, default CRS settings: passed (0 of 1 requests blocked), template CVE-2021-33766, 2026-11-02

"No public claim" means no vendor statement names this CVE; "Before feed history" means the CVE is older than the vendor feed. In both cases generic rules may still block it.

HTML: https://cve.vigilbase.com/cve/CVE-2021-33766 · JSON: https://cve.vigilbase.com/api/v1/cves/CVE-2021-33766