CVE-2026-55005: Heap-based buffer overflow in Microsoft Exchange Server allows an authorized attacker to execute code over a n

Q: How do I fix CVE-2026-55005?

exchange server: downgrade or apply the listed mitigation; exchange server subscription edition: upgrade to 15.02.2562.045. Exact commands for each OS are on this page.

Q: Is CVE-2026-55005 being exploited?

CVE-2026-55005 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-55005 affect?

CVE-2026-55005 affects exchange server, exchange server subscription edition. Severity is high (CVSS 8.8). Heap-based buffer overflow in Microsoft Exchange Server allows an authorized attacker to execute code over a network.

Q: How urgent is CVE-2026-55005?

Priority 52/100. High severity; On your watchlist

This month

HIGH 8.8WATCHLISTDOWNGRADEUPGRADE

CVE-2026-55005 is a high-severity flaw (CVSS 8.8) affecting exchange server, exchange server subscription edition. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Heap-based buffer overflow in Microsoft Exchange Server allows an authorized attacker to execute code over a network.

Why this priority

High severity
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	8.8 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	1.0% (top 37%)
CISA exploited list	No
Weakness	CWE-122
Published	2026-07-14
Last modified	2026-10-14

Publisher (CNA): Microsoft Corporation · Vendor: microsoft

Last updated 2026-10-14 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-14 17:17 UTCPublished CVE record published
2026-10-14 22:10 UTCUpdated Record last modified

microsoft exchange server DOWNGRADE

Affected: 2016 cumulative_update_23 · 2019 cumulative_update_14 · 2019 cumulative_update_15

Fixed in: no fixed release known

Safe to downgrade to: a release before 2016

1. Check installed version

apt-cache policy exchange-server || rpm -q exchange-server || exchange-server --version

2. No fixed release: DOWNGRADE to a release before 2016 (Debian / Ubuntu)

apt-cache madison exchange-server sudo apt install exchange-server=<VERSION_BEFORE_2016> sudo apt-mark hold exchange-server

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list exchange-server sudo dnf downgrade exchange-server-<VERSION_BEFORE_2016> sudo dnf versionlock add exchange-server

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

microsoft exchange server subscription edition UPGRADE

Affected: < 15.02.2562.045

Fixed in: 15.02.2562.045

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy exchange-server-subscription-edition || rpm -q exchange-server-subscription-edition || exchange-server-subscription-edition --version

2. UPGRADE to 15.02.2562.045 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade exchange-server-subscription-edition

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade exchange-server-subscription-edition

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-55005?

exchange server: downgrade or apply the listed mitigation; exchange server subscription edition: upgrade to 15.02.2562.045. Exact commands for each OS are on this page.

Is CVE-2026-55005 being exploited?

CVE-2026-55005 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-55005 affect?

CVE-2026-55005 affects exchange server, exchange server subscription edition. Severity is high (CVSS 8.8). Heap-based buffer overflow in Microsoft Exchange Server allows an authorized attacker to execute code over a network.

How urgent is CVE-2026-55005?

Priority 52/100. High severity; On your watchlist

Software pages

Microsoft Exchange vulnerabilities

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References

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