Microsoft Exchange Server Subscription Edition RTM: attackers can run their own code
OFFICIAL NAME: Microsoft Exchange Server Remote Code Execution Vulnerability
WHAT IT IS · EMAILIt carries internal and customer mail.
DO THIS FIRSTPatch it, or ask your email provider whether they have. Not sure if you use it? Send this page to your IT provider or security lead and ask.
TECHNICAL SUMMARY Improper input validation in Microsoft Exchange Server allows an authorized attacker to execute code over a network.
WHY THIS VERDICT One source reports attacks and the vulnerability is new today. In our backtest a single early report was confirmed within 30 days about one time in twenty, so we wait for a second report or for attack attempts to be seen.
WHY IT RANKS HERE Exploitation is reported. The product faces the internet or gives remote access. The first report is from today.
- HIGHEST CONFIRMED RUNG
- NOTHING YET
- CISA KEV
- NOT YET
- EXPLOIT CODE
- NONE KNOWN
How far has it climbed?
01 TALK
□ NO EVIDENCE YETNEWEST EVIDENCE NONE YETNo evidence yet.
SRC: NONE YET02 EXPOSED
□ NOT TRACKED YETNO SOURCE FOR THIS STEP YETWe have no source that counts exposed systems yet. Internet scan data needs a partnership we do not have. No evidence here does not mean nothing is exposed.
03 TRIED
▨ REPORTED, NOT CONFIRMEDNEWEST EVIDENCE · 1 SOURCEAttacks that worked are reported (step 4), so attempts count as reported too.
04 EXPLOITED
▨ REPORTED, NOT CONFIRMEDNEWEST EVIDENCE · 1 SOURCEExploitation of CVE-2026-118207 reported (CIRCL sighting).
05 DAMAGE
□ NOT TRACKED YETNO SOURCE FOR THIS STEP YETBreach notices and filings rarely name the flaw that was used, so we cannot link them to this event yet. No evidence here does not mean no harm.
When each thing happened
- DISCLOSED
- EXPLOIT CODE PUBLICNOT YET
- FIRST ATTACK REPORT
- CISA KEV LISTINGNOT YET
- US FEDERAL DEADLINENOT YET
Questions to ask this week
- Do we run Microsoft Exchange Server Subscription Edition RTM? If yes, is it patched or cut off from the internet?
- Who owns fixing it, and by what date?
- Have we checked for signs of attack since the first report, not just since the patch?
How it unfolded
- Attack activity. NOV 10, 2026Exploitation of CVE-2026-118207 reported (CIRCL sighting)