CVE-2021-26855
Act now ● On CISA KEV — actively exploited used in ransomware
Actively exploited — on the CISA KEV list.
CVSS base
9.1
CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
EPSS — probability of exploitation (30 days)
100.0%
100.0th percentile
CISA KEV
Listed
Added 2021-11-03 · patch by 2022-05-03
Weakness / dates
CWE-918
Published 2021-03-03 · modified 2026-08-19
CVSS breakdown
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
| Attack Vector | N | Network |
| Attack Complexity | L | Low |
| Privileges Required | N | None |
| User Interaction | N | None |
| Scope | U | Unchanged |
| Confidentiality | H | High |
| Integrity | H | High |
| Availability | N | None |
Timeline
- 2021-03-03 — Published (NVD)
- 2021-11-03 — Added to CISA KEV (actively exploited)
- 2022-05-03 — CISA patch-by deadline
- 2026-08-19 — Last modified (NVD)
Description
Microsoft Exchange Server Remote Code Execution Vulnerability
Affected
References
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26855
- exploit http://packetstormsecurity.com/files/161846/Microsoft-Exchange-2019-SSRF-Arbitrary-File-Write.html
- exploit http://packetstormsecurity.com/files/161938/Microsoft-Exchange-ProxyLogon-Remote-Code-Execution.html
- exploit http://packetstormsecurity.com/files/162610/Microsoft-Exchange-2019-Unauthenticated-Email-Download.html
- exploit http://packetstormsecurity.com/files/162736/Microsoft-Exchange-ProxyLogon-Collector.html
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26855
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26855