CVE-2021-26411Microsoft Internet Explorer Memory Corruption Vulnerability
CVE-2021-26411 is a use after free in Microsoft Internet Explorer, rated high (8.8 on CVSS 3.1).
Why this priority: Exploited in the wild: listed in CISA's KEV catalog.
Published · Updated · NVD status: Analyzed
What it is
Code keeps using memory after releasing it, so an attacker who refills that memory can steer execution.
How it is reached
An attacker can exploit it over the network, without an account, but someone has to act first, such as opening a file or following a link.
What an attacker gains
A successful attack can change data or behaviour. In practice, this kind of flaw lets an attacker crash the process, read memory, or in the worst case run code. The damage can spread past the vulnerable component into others.
Is it being exploited?
CISA added it to the Known Exploited Vulnerabilities catalog on 2021-11-03: it is being exploited in the wild. CISA links it to ransomware campaigns. EPSS estimates a 82% chance of exploitation activity in the next 30 days, higher than 100% of scored CVEs.
What to do
- Treat it as urgent: it is on CISA's KEV list. CISA's deadline for US federal agencies: 2021-11-17.
- Apply the update for your edition of Microsoft Internet Explorer. Fixed builds: Internet Explorer 11: 10.0.17134.2087; Internet Explorer 9: 6.0.6003.21070. Other affected products have their own fixed versions on this page. The patch notes are linked below.
- Until it is patched, keep it off the internet or behind a VPN, allowlist or authenticating proxy.
- Warn the people who use it, and filter files and links on the way in.
- Check exposed instances for signs of compromise, not only for the version.
Description from NVD
Internet Explorer Memory Corruption Vulnerability
What this means for your architecture.
A CVE names a product. Whether it matters depends on where that product sits in your systems: what reaches it, which trust boundary it guards and what it can reach once compromised. Veriom maps your components, their relationships and your trust boundaries from your code, cloud and delivery evidence, so you can see where a component like this sits. The radar itself does not look at your systems.
Components it touches
- Native code: operating systems, browsers and firmware. The flaw sits wherever native code reads untrusted data.
- Network appliances and media or file parsers. The flaw sits wherever native code reads untrusted data.
Trust boundaries in play
- Internet-facing entry points. No account is needed. Any instance reachable from outside your perimeter, through a load balancer, gateway, VPN or exposed admin port, is in scope.
- People who open files and links. Mail, chat and browsers are the delivery path.
- Isolation between components. The impact crosses out of the vulnerable component into others it should be isolated from.
- Wherever native code reads untrusted data. An attacker who crosses it can crash the process, read memory, or in the worst case run code.
Questions to answer about your own systems
- Where does Microsoft Internet Explorer run in your systems, and at which version?
- Which of those instances can be reached from the internet or partner networks?
- What can it reach once compromised: which data stores, secrets and services?
Sources
- CVE records and CVSS scores from the NVD CVE API. This product uses the NVD API but is not endorsed or certified by the NVD.
- Exploitation status from CISA’s Known Exploited Vulnerabilities catalog.
- Exploit likelihood from FIRST’s Exploit Prediction Scoring System (EPSS), refreshed daily.
- Explanations are written by Veriom from fixed templates over each record’s data, not by a person reviewing each CVE. Descriptions are quoted from the records as published.