Microsoft Internet Explorer Memory Corruption
CVE-2021-26411 is a high-severity use after free vulnerability in Internet Explorer 11 from Microsoft, with a CVSS 3.1 base score of 8.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, but only if a user takes part, for example by opening a link or file. The record lists version 10.0.17134.2087 as the first without the flaw, so updating Internet Explorer 11 to that release or later removes the exposure. CISA added it to the Known Exploited Vulnerabilities catalogue on November 3, 2021, which means attacks have been observed in the wild, including in ransomware campaigns.
Attackers are already exploiting this vulnerability, according to CISA.
What to do
- Update Internet Explorer 11 to 10.0.17134.2087 or a later version.
- Update Internet Explorer 9 to 6.0.6003.21070 or a later version.
- Update Microsoft Edge (EdgeHTML-based) to 10.0.17134.2087 or a later version.
- CISA's required action: Apply updates per vendor instructions.
- Read the advisory on msrc.microsoft.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
- Because the attack needs a user to take part, warn users about unexpected links and files related to this product until it is patched.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Microsoft | Internet Explorer 11 | 1.0.0 up to, but not including, 10.0.17134.2087 | 10.0.17134.2087 |
| Microsoft | Internet Explorer 9 | 1.0.0 up to, but not including, 6.0.6003.21070 | 6.0.6003.21070 |
| Microsoft | Microsoft Edge (EdgeHTML-based) | 1.0..0 up to, but not including, 10.0.17134.2087 | 10.0.17134.2087 |
| Microsoft | Edge | Not specified in the record | Not stated |
| Microsoft | Internet Explorer | 11; 9 | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- RequiredA user must take an action such as opening a file or link.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 8.8 | High | CNA (microsoft.com) |
| CVSS 3.1 | 8.8 | High | NVD |
| CVSS 2.0 | 5.1 | Medium | NVD |
Official description
Internet Explorer Memory Corruption Vulnerability
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Use After Free
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.
How developers prevent this class of flaw
- Choose a language that provides automatic memory management.
- When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.
Timeline
- CVE record published.
- Added to CISA's Known Exploited Vulnerabilities catalogue.
- Deadline for US federal agencies to remediate, set by CISA.
- CISA published its SSVC assessment (exploitation: active, automatable: no, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Advisories
Third-party and government advisories
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26411US Government Resource
Other vulnerabilities in Internet Explorer 11
- 8.8 High severity
- 7.5 High severity
- 8.8 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
Recent Use After Free vulnerabilities
- 8.8 High severity
Google Chrome Media Use-After-Free Exploited
- 9.6 Critical severity
Google Chrome Use-After-Free Exploited
- 9.8 Critical severity
VMware ESXi OpenSLP Use-After-Free Exploited
- 7.8 High severity
Adobe Acrobat Use-After-Free Exploited
- 7.8 High severity
Apple Multiple Products Use-After-Free Exploited
- 7.8 High severity
Apple macOS Use-After-Free Exploited
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