CVE-2021-26857

Microsoft Exchange Server: Remote Code Execution

As of , CVE-2021-26857 in Microsoft Exchange Server is on CISA's list of exploited vulnerabilities: CISA listed it on . Our patch-first group: Patch this week.

Exploited
Yes: CISA listed it on 3 November 2021
US federal deadline
3 May 2022181 days after CISA listed it. US federal civilian agencies must fix it by then.
Used in ransomware campaigns
Known
EPSS score
0.96Higher than 99% of the CVEs EPSS scores. EPSS estimates the chance of exploitation activity in the next 30 days.
EPSS when listed
Not availableCISA listed it before 4 February 2022, where the EPSS files we read begin.
Public exploit
None foundNeither Metasploit nor Exploit-DB lists one.
Fix
No vendor link in CISA's entry

What CISA says to do

Apply updates per vendor instructions.

CISA's required action

What the flaw is

Microsoft Exchange Server contains an unspecified vulnerability that allows for remote code execution. This vulnerability is part of the ProxyLogon exploit chain.

CISA's description

Microsoft Exchange Server Remote Code Execution Vulnerability

The CVE record's description, from microsoft

CVE published
2 March 2021
Assigned by
microsoft
CVSS
7.8 High (CVSS 3.1, from the CNA)
CWE-502
Deserialization of Untrusted Data
CISA SSVC, exploitation
active
CISA SSVC, automatable
no
CISA SSVC, technical impact
total

Timeline

  1. The CVE record was published.
  2. CISA added it to its list of exploited vulnerabilities.
  3. The US federal deadline to fix it.
  4. CISA changed its entry. Deadline moved from 16 April 2021 to 3 May 2022.

Exchange Server: other exploited entries

VulnerabilityProductOur groupListedDeadlineEPSS
CVE-2023-21529Deserialization of Untrusted DataMicrosoft Exchange ServerPatch nowRansomware use, listed within a year0.59
CVE-2020-0688Validation Key Remote Code ExecutionMicrosoft Exchange ServerPatch this weekRansomware use; Metasploit module; EPSS 0.99; verified Exploit-DB entry0.99
CVE-2022-41040Server-Side Request ForgeryMicrosoft Exchange ServerPatch this weekRansomware use; Metasploit module; EPSS 0.990.99
CVE-2022-41082Remote Code ExecutionMicrosoft Exchange ServerPatch this weekRansomware use; Metasploit module; EPSS 0.990.99
CVE-2021-26855Remote Code ExecutionMicrosoft Exchange ServerPatch this weekRansomware use; Metasploit module; EPSS 0.990.99
CVE-2021-27065Remote Code ExecutionMicrosoft Exchange ServerPatch this weekRansomware use; Metasploit module; EPSS 0.990.99
CVE-2021-31207Security Feature BypassMicrosoft Exchange ServerPatch this weekRansomware use; Metasploit module; EPSS 0.990.99
CVE-2021-34473Remote Code ExecutionMicrosoft Exchange ServerPatch this weekRansomware use; Metasploit module; EPSS 0.990.99
CVE-2021-34523Privilege EscalationMicrosoft Exchange ServerPatch this weekRansomware use; Metasploit module; EPSS 0.990.99
CVE-2022-41080Privilege EscalationMicrosoft Exchange ServerPatch this weekRansomware use; EPSS 0.770.77

All 17 entries for Exchange Server

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