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CVE-2026-66302: External control of file name or path in Skype for Business allows an unauthorized attacker to execute code ov

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This week
CRITICAL 9.8REMOTEWATCHLISTDOWNGRADEDOWNGRADE

CVE-2026-66302 is a critical-severity flaw (CVSS 9.8) affecting skype for business server, skype for business server subscription edition. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

External control of file name or path in Skype for Business allows an unauthorized attacker to execute code over a network.

Why this priority

  • Critical severity
  • CISA SSVC: automatable with total technical impact
  • Remotely exploitable, no login, no user action
  • On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score9.8 (Critical)
Attack vectorNetwork (remote)
Attack complexityLow
Privileges neededNone
User interactionNone
EPSS exploit chance1.0% (top 38%)
CISA exploited listNo
WeaknessCWE-73
Published2026-09-08
Last modified2026-09-16
Publisher (CNA): Microsoft Corporation · Vendor: microsoft

Share: LinkedIn · X · Reddit

Last updated 2026-09-16 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

microsoft skype for business server DOWNGRADE
Affected: 2015 cumulative_update_13 · 2015 cumulative_update_13_hotfix_2 · 2019 cumulative_update_8 · 2019 cumulative_update_8_hotfix1 · 2019 cumulative_update_8_hotfix2
Fixed in: no fixed release known
Safe to downgrade to: a release before 2015
1. Check installed version
apt-cache policy skype-for-business-server || rpm -q skype-for-business-server || skype-for-business-server --version
2. No fixed release: DOWNGRADE to a release before 2015 (Debian / Ubuntu)
apt-cache madison skype-for-business-server sudo apt install skype-for-business-server=<VERSION_BEFORE_2015> sudo apt-mark hold skype-for-business-server
2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list skype-for-business-server sudo dnf downgrade skype-for-business-server-<VERSION_BEFORE_2015> sudo dnf versionlock add skype-for-business-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 skype for business server subscription edition DOWNGRADE
Affected: 7.0.2046.849
Fixed in: no fixed release known
Safe to downgrade to: a release before 7.0.2046.849
1. Check installed version
apt-cache policy skype-for-business-server-subscription-edition || rpm -q skype-for-business-server-subscription-edition || skype-for-business-server-subscription-edition --version
2. No fixed release: DOWNGRADE to a release before 7.0.2046.849 (Debian / Ubuntu)
apt-cache madison skype-for-business-server-subscription-edition sudo apt install skype-for-business-server-subscription-edition=<VERSION_BEFORE_7.0.2046.849> sudo apt-mark hold skype-for-business-server-subscription-edition
2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list skype-for-business-server-subscription-edition sudo dnf downgrade skype-for-business-server-subscription-edition-<VERSION_BEFORE_7.0.2046.849> sudo dnf versionlock add skype-for-business-server-subscription-edition
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.

Exact fixes by distribution

A distro patch exists: prefer upgrading over downgrading.
Fedora ELN · xfsdump · FIXED · 3.3.0-3.eln159 · FEDORA-2026-6e9bb3f901 · source
sudo dnf upgrade --advisory=FEDORA-2026-6e9bb3f901
Fedora 46 · fio · FIXED · 3.43-2.fc46 · FEDORA-2026-b36219886b · source
sudo dnf upgrade --advisory=FEDORA-2026-b36219886b
Skype for Business Server 2019 CU8 · KB5123300 · FIXED · 7.0.2046.569 · KB5123300
Install KB5123300 via Windows Update, then verify: Get-HotFix -Id KB5123300
Skype for Business Server Subscription Edition CU1 · KB5123287 · FIXED · 7.0.2046.879 · KB5123287 · source
Install KB5123287 via Windows Update, then verify: Get-HotFix -Id KB5123287
Skype for Business Server 2015 CU13 · KB5123301 · FIXED · 6.0.9319.885 · KB5123301
Install KB5123301 via Windows Update, then verify: Get-HotFix -Id KB5123301
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-2026-66302?

skype for business server: downgrade or apply the listed mitigation; skype for business server subscription edition: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2026-66302 being exploited?

CVE-2026-66302 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-2026-66302 affect?

CVE-2026-66302 affects skype for business server, skype for business server subscription edition. Severity is critical (CVSS 9.8). External control of file name or path in Skype for Business allows an unauthorized attacker to execute code over a network.

How urgent is CVE-2026-66302?

Priority 63/100. Critical severity; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action; On your watchlist

Related CVEs

References

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