Security Resilience

CVE-2021-26411

Memory Safety in Microsoft Internet Explorer 11 … 9

CISA KEVActive ExploitationEUVD ExploitedRansomware-linkedMemory Safety
Published
11 March 2021
Modified
01 October 2026
KEV Added
03 November 2021
Patch / advisory
View advisory
CVSS Score v3.1 8.8
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L
EPSS Score 0.81 99.6th percentile
Risk Priority 88 floored blend · peak EPSS

CVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.

Summary

CVE-2021-26411 is a high-severity Use After Free (CWE-416) vulnerability in Microsoft Windows 10 1903. Its CVSS base score is 8.8 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique OS Credential Dumping (T1003); ranked in the top 0.4% of CVEs by exploit likelihood; CISA has added it to the Known Exploited Vulnerabilities catalog.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

CVE-2021-26411 is a memory corruption vulnerability, specifically a use-after-free issue tracked under CWE-416, that affects Internet Explorer. It received a CVSS v3.1 base score of 8.8 with the vector string AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L, indicating a remotely exploitable flaw in the browser's handling of certain objects or resources.

An attacker can exploit the vulnerability by serving specially crafted web content that triggers the memory corruption condition when rendered in Internet Explorer. Successful exploitation allows the attacker to achieve altered memory state that may lead to arbitrary code execution or other impacts within the browser process, with the changed scope metric reflecting potential effects beyond the immediate IE sandbox.

Microsoft published an advisory detailing the issue and available updates, while CISA lists the CVE in its catalog of known exploited vulnerabilities in the wild, confirming active targeting by adversaries. Security practitioners should prioritize applying the vendor patches referenced in the Microsoft Security Response Center guidance to address the flaw.

EU & UK References

Vulnerability Data

Internet Explorer Memory Corruption Vulnerability

CWE(s)
CWE-416
KEV Date Added
03 November 2021

Related Threats

MITRE ATT&CK Enterprise Techniques

T1003 OS Credential Dumping Credential Access
Adversaries may attempt to dump credentials to obtain account login and credential material, normally in the form of a hash or a clear text password.
attack.mitre.org →
T1003.001 LSASS Memory Credential Access
Adversaries may attempt to access credential material stored in the process memory of the Local Security Authority Subsystem Service (LSASS).
attack.mitre.org →
T1003.004 LSA Secrets Credential Access
Adversaries with SYSTEM access to a host may attempt to access Local Security Authority (LSA) secrets, which can contain a variety of different credential materials, such as credentials for service accounts.
attack.mitre.org →
T1007 System Service Discovery Discovery
Adversaries may try to gather information about registered local system services.
attack.mitre.org →
T1008 Fallback Channels Command And Control
Adversaries may use fallback or alternate communication channels if the primary channel is compromised or inaccessible in order to maintain reliable command and control and to avoid data transfer thresholds.
attack.mitre.org →
T1011 Exfiltration Over Other Network Medium Exfiltration
Adversaries may attempt to exfiltrate data over a different network medium than the command and control channel.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2020-0674Same product: Microsoft Internet Explorerboth on KEV
CVE-2021-40449Same product: Microsoft Windows 10 1507both on KEV
CVE-2017-0263Same product: Microsoft Windows 10 1507both on KEV
CVE-2023-21674Same product: Microsoft Windows 10 1507both on KEV
CVE-2019-1429Same product: Microsoft Internet Explorerboth on KEV
CVE-2025-24983Same product: Microsoft Windows 10 1507both on KEV
CVE-2023-29336Same product: Microsoft Windows 10 1507both on KEV
CVE-2013-3897Same product: Microsoft Internet Explorerboth on KEV
CVE-2024-38193Same product: Microsoft Windows 10 1507both on KEV
CVE-2025-32701Same product: Microsoft Windows 10 1507both on KEV

Affected Assets

microsoft
edge
all versions
microsoft
internet explorer
11, 9

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)
  • 3 hardening rules · 3 OS baselines
Validate
Prove the fix (OWASP ASVS)
  • V1.4.3

Likely Mitigating Controls AI

Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.

SI-16 Memory Protection
addresses: CWE-416

Use-after-free exploits that achieve arbitrary code execution are blocked or significantly hardened by non-executable pages and ASLR.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

ID.RA-01 partial match
blocks

Vulnerability identification processes can discover use-after-free issues via scanning or analysis but do not prevent their introduction.

PR.PS-02 partial match
blocks

Routine patching removes known use-after-free instances after they have been introduced in released software.

PR.PS-06 partial match
blocks

Secure SDLC practices directly incorporate memory-safety tooling and reviews that prevent most use-after-free defects.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.5.14 Information transfer partial match
removes
A.5.15 Access control partial match
removes
A.5.16 Identity management partial match
removes
A.5.17 Authentication information partial match
removes
A.5.18 Access rights partial match
removes
A.5.30 ICT readiness for business continuity partial match
removes

Hardening callouts derived

Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (higher-evidence rows only; rows rated `none` are excluded).

Oracle Linux 8 (1 rule)
  • V-248592 OL 8 must clear memory when it is freed to prevent use-after-free attacks. blocks CWE-416
RHEL 8 (1 rule)
  • V-230279 RHEL 8 must clear memory when it is freed to prevent use-after-free attacks. blocks CWE-416
RHEL 9 (1 rule)
  • V-257794 RHEL 9 must clear memory when it is freed to prevent use-after-free attacks. blocks CWE-416

References