Vulnerability record

CVE-2021-26858

A permanent, source-backed tracker page. Values are shown only when returned; explicit gaps and read failures remain different states.

Full record read. Reported values and explicit gaps below come from the tracked record. Tracker snapshot: Aug 8, 2026.

What it is

Reported

Microsoft Exchange Server contains an unspecified vulnerability that allows for remote code execution. This vulnerability is part of the ProxyLogon exploit chain. Source description excerpt; complete tracked detail loads below.

NVD published: Mar 3, 2021 · Source record updated: Aug 8, 2026 · Tracker snapshot: Aug 8, 2026

What is affected

Reported

Microsoft — Exchange Server. Product-level identification only; no affected-version conclusion is available from this field.

NVD published: Mar 3, 2021 · Source record updated: Aug 8, 2026 · Tracker snapshot: Aug 8, 2026

Urgency and basis

Reported

Act now · 567.0

Tracker decision tier from the evidence detailed below · Source record updated: Aug 8, 2026 · Tracker snapshot: Aug 8, 2026

Exploitation evidence

Reported

Active exploitation · CISA KEV · VulnCheck KEV · ENISA exploited-vulnerability catalog

Active since: Nov 3, 2021 · CISA KEV added: Nov 3, 2021 · VulnCheck KEV added: Mar 2, 2021 · ENISA added: Nov 3, 2021 · Source record updated: Aug 8, 2026 · Tracker snapshot: Aug 8, 2026

What to do

Reported

Apply updates per vendor instructions.

Source remediation ↗

Tracked source remediation field · Source record updated: Aug 8, 2026 · Tracker snapshot: Aug 8, 2026

Evidence detail

Loading the full tracker evidence record…