CVE-2021-26411: Microsoft Internet Explorer Memory Corruption Vulnerability

Patch now

HIGH 8.8EXPLOITEDWATCHLISTMITIGATEDOWNGRADE

CVE-2021-26411 is a high-severity flaw (CVSS 8.8) affecting edge, internet explorer, reported as exploited in the wild. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Internet Explorer Memory Corruption Vulnerability

Why this priority

High severity
EPSS top 1%: very likely to be exploited
Exploited in the wild (CISA KEV)
Used in ransomware campaigns
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	None
User interaction	Required
EPSS exploit chance	81.7% (top 1%)
CISA exploited list	Yes, fix due 2021-11-17, used in ransomware
Weakness	CWE-416
Published	2021-03-11
Last modified	2026-10-01

Publisher (CNA): Microsoft Corporation · Vendor: microsoft

Last updated 2026-10-01 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-03-11 16:15 UTCPublished CVE record published
2021-11-03Exploited Added to the CISA Known Exploited Vulnerabilities list
2021-11-17Deadline CISA due date for US federal agencies to patch
2026-10-01 21:17 UTCUpdated Record last modified

microsoft edge MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy edge || rpm -q edge || edge --version

No fixed or unaffected release known

Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.

microsoft internet explorer DOWNGRADE

Affected: 11 · 9

Fixed in: no fixed release known

Safe to downgrade to: a release before 9

1. Check installed version

apt-cache policy internet-explorer || rpm -q internet-explorer || internet-explorer --version

2. No fixed release: DOWNGRADE to a release before 9 (Debian / Ubuntu)

apt-cache madison internet-explorer sudo apt install internet-explorer=<VERSION_BEFORE_9> sudo apt-mark hold internet-explorer

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

dnf --showduplicates list internet-explorer sudo dnf downgrade internet-explorer-<VERSION_BEFORE_9> sudo dnf versionlock add internet-explorer

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 46 · bitcoin-core-selinux · FIXED · 0.3-2.fc46 · FEDORA-2026-51fc806272 · source

sudo dnf upgrade --advisory=FEDORA-2026-51fc806272

Fedora ELN · guestfs-tools · FIXED · 1.57.5-1.eln159 · FEDORA-2026-9577c5ec16 · source

sudo dnf upgrade --advisory=FEDORA-2026-9577c5ec16

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

GitHub PoC: CrackerCat/CVE-2021-26411 (2 stars)

Verify at the official source NVD · CVE Program · CISA KEV catalog · 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-2021-26411?

edge: mitigate or apply the listed mitigation; internet explorer: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-26411 being exploited?

Yes. CVE-2021-26411 is on the CISA Known Exploited Vulnerabilities list, so treat it as patch-now.

What does CVE-2021-26411 affect?

CVE-2021-26411 affects edge, internet explorer. Severity is high (CVSS 8.8). Internet Explorer Memory Corruption Vulnerability

How urgent is CVE-2021-26411?

Priority 91/100. High severity; EPSS top 1%: very likely to be exploited; Exploited in the wild (CISA KEV); Used in ransomware campaigns; On your watchlist

Software pages

Microsoft Edge vulnerabilities · Internet Explorer vulnerabilities

Related CVEs

CVE-2026-83831 HIGH 8.8 UPGRADE Double free in Microsoft Edge (Chromium-based) allows an unauthorized attacker to execute code over a network.
CVE-2026-85898 HIGH 8.8 UPGRADE Access of resource using incompatible type ('type confusion') in Microsoft Edge (Chromium-based) allows an una
CVE-2026-62765 HIGH 7.5 UPGRADE Access of resource using incompatible type ('type confusion') in Microsoft Edge (Chromium-based) allows an una
CVE-2026-85330 MEDIUM 4.3 UPGRADE Incorrect authorization in Microsoft Edge for Android allows an unauthorized attacker to bypass a security fea
CVE-2026-96192 HIGH 8.8 UPGRADE Use after free in Microsoft Edge for iOS allows an unauthorized attacker to execute code over a network.

References

← Back to latest CVEs