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CVE-2021-26411· NVD / CVE Program· CNA microsoft

Internet Explorer Memory Corruption Vulnerability

HighCVSS 8.8 · v3.1KEVWeaponized No fix recorded
Published
Mar 11, 2021
Updated
Aug 19, 2026
EPSS
80.8% · 100th percentile
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Action score

89

Now

Patch today or shut off access.

CVSS
35 / 40 · 8.8 / 10
CISA KEV
30 / 30 · Listed
EPSS
24 / 30 · 80.8%

CISA SSVC decision

Exploitation
active
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · microsoft
8.8
NVD has not scored this yet; the score shown is the CNA’s.

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L/E:P/RL:O/RC:C

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Actively exploited in the wild

CISA added this to its Known Exploited Vulnerabilities catalog on Nov 3, 2021. That signals real attacks, not theory.

Remediation deadline for government agencies: Nov 17, 2021.

Known to be used in ransomware campaigns.

Affected systems

VendorProduct
microsoftedge
microsoftwindows 10 1507
microsoftwindows 10 1607
microsoftwindows 10 1803
microsoftwindows 10 1809
microsoftwindows 10 1903
microsoftwindows 10 1909
microsoftwindows 10 2004
microsoftwindows 10 20h2
microsoftwindows server 2016
microsoftwindows server 2019
microsoftinternet explorer

and 5 more

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • microsoft edgeall versions
  • microsoft internet explorer11
  • microsoft internet explorer9

Versions reported by the vendor

Affected version ranges reported by the assigning authority (microsoft). Independent of NVD's CPE analysis and usually ahead of it.

  • Microsoft Internet Explorer 11

    • 1.0.0 and later · before 10.0.17134.2087affected

  • Microsoft Internet Explorer 9

    • 1.0.0 and later · before 6.0.6003.21070affected

  • Microsoft Microsoft Edge (EdgeHTML-based)

    • 1.0..0 and later · before 10.0.17134.2087affected

Same product

microsoft: all records

Other highest-scoring records for the same primary product.

  • CVE-2016-7200The Chakra JavaScript scripting engine in Microsoft Edge allows remote attackers to execute arbitrary code or cause a denial of service (memKEV
    90Now
  • CVE-2016-7201The Chakra JavaScript scripting engine in Microsoft Edge allows remote attackers to execute arbitrary code or cause a denial of service (memKEV
    89Now
  • CVE-2017-0037Microsoft Internet Explorer 10 and 11 and Microsoft Edge have a type confusion issue in the Layout::MultiColumnBoxBuilder::HandleColumnBreakKEV
    86Now
  • CVE-2018-0777Microsoft Edge in Windows 10 Gold, 1511, 1607, 1703, 1709, and Windows Server 2016 allows an attacker to execute arbitrary code in the conte
    54Plan
  • CVE-2018-0776Microsoft Edge in Windows 10 Gold, 1511, 1607, 1703, 1709, and Windows Server 2016 allows an attacker to execute arbitrary code in the conte
    54Plan
  • CVE-2018-0770Microsoft Edge in Windows 10 Gold, 1511, 1607, 1703, 1709, and Windows Server 2016 allows an attacker to execute arbitrary code in the conte
    54Plan

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

No fix version is recorded for this entry. Check the references for vendor advisories.

Exploit status

Weaponized

A ready exploit tool or active in-the-wild use is known for this vulnerability. This should be your top priority.

Evidence

  • Proof-of-concept repository on GitHub ×1

Noroxi does not host or link to exploit code. Metasploit module names and Nuclei template ids are shown (names, not code); Exploit-DB entries and PoC repositories are given as counts only.

Public exploit evidence
SourceKindDate
Proof-of-concept repository on GitHubstars:22021-11-22

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

  1. Published
  2. CISA KEV+236 d
  3. First PoC+255 d
  4. TodaySep 29, 2026+2028 d
EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • A user must open a link or visit a page.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
low · data can be read
Integrity
high · data or configuration can be modified
Availability
low · the service can be disrupted

Impact can extend beyond the vulnerable component (scope changes).

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
Required
Scope
Changed
Confidentiality impact
Low
Integrity impact
High
Availability impact
Low

Weakness class (CWE)

CWE-416 · Use After Free

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L

nvd-secondary

Root cause

After a memory region is freed, another reference pointing to it is still used. By then, the same region may have been allocated for different data.

The bug in code

The whole CWE-416 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

c
free(dev->buf);/* ... another thread is still running ... */process(dev->buf);

Fixed

c
lock(&dev->lock);free(dev->buf);dev->buf = NULL;unlock(&dev->lock);

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Noroxi analysis

No Noroxi analysis for this record yet

We don't hand-write analysis for all 385,000+ vulnerabilities; that wouldn't be honest. For notable, high-impact vulnerabilities our team writes the mechanism, detection and remediation steps.

We use this product, ask for help

Change log

No changes recorded on tracked fields yet. Score, KEV, exploit maturity and fix status changes appear here.

References

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records