Affects Microsoft Exchange Server — widely deployed enterprise mail server; RCE in Exchange can lead to domain-wide compromise and major operational impact.
CVE-2026-55005
Authenticated heap-buffer-overflow RCE in Microsoft Exchange Server.
Is CVE-2026-55005 being exploited?
Not confirmed. CVE-2026-55005 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 1.0% probability of exploitation in the next 30 days.
How severe is CVE-2026-55005?
CVE-2026-55005 is rated High with a CVSS score of 8.8. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-55005?
Yes. A fix has been recorded for CVE-2026-55005. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-55005 affect?
CVE-2026-55005 affects Microsoft Exchange Server (on-premises). Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-55005?
Apply vendor patch immediately when released; isolate Exchange, block external OWA/ECP, and monitor logs.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Authenticated attacker can trigger a heap overflow to achieve remote code execution, full server compromise, and potential domain pivot.
Immediate action required
- affected>= 15.01.0.0 and < 15.01.2507.071
- affected>= 15.02.0.0 and < 15.02.1544.043
- affected>= 15.02.0.0 and < 15.02.1748.048
- affected>= 15.02.0.0 and < 15.02.2562.045
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.