CVE-2021-34448
Scripting Engine Memory Corruption Vulnerability
- CVSS
- 6.8Mediumscored by the publisher (CNA)
- Exploited in the wild
- Yes, in CISA KEV since 3 Nov 2021CISA deadline for US federal agencies: 17 Nov 2021
- EPSS
- 40.1%chance of exploitation in the next 30 daystop 2% of scored CVEsFIRST score of 11 Nov 2026
- Fix
- Patch availablesee the advisories in the references
- Published
- 16 Jul 2021analysed here 12 Nov 2026
Do first. Apply updates per vendor instructions. (CISA's required action for this KEV entry)
Summary
Triage
The summary, impact and action text on this page are written by our AI analysis pipeline, or taken from the NVD description when a CVE was imported from NVD. They are not the vendor's wording: check them against the sources. A longer AI executive summary and technical analysis are generated for signed-in accounts on the Max plan.
Affected products
| Product | Affected versions | Vendor says fixed in |
|---|---|---|
| Microsoft Windows 10 Version 1507 | >= 10.0.10240.0 and < 10.0.10240.19003Vendor says fixed in: not stated | |
| Microsoft Windows 10 Version 1607 | >= 10.0.14393.0 and < 10.0.14393.4530Vendor says fixed in: not stated | |
| Microsoft Windows 10 Version 1809 | >= 10.0.17763.0 and < 10.0.17763.2061>= 10.0.0 and < 10.0.17763.2061Vendor says fixed in: not stated | |
| Microsoft Windows 10 Version 1909 | >= 10.0.0 and < 10.0.18363.1679Vendor says fixed in: not stated | |
| Microsoft Windows 10 Version 2004 | >= 10.0.0 and < 10.0.19041.1110Vendor says fixed in: not stated | |
| Microsoft Windows 10 Version 20H2 | >= 10.0.0 and < 10.0.19042.1110Vendor says fixed in: not stated | |
| Microsoft Windows 10 Version 21H1 | >= 10.0.0 and < 10.0.19043.1110Vendor says fixed in: not stated | |
| Microsoft Windows 7 | >= 6.1.0 and < 6.1.7601.25661Vendor says fixed in: not stated | |
| Microsoft Windows 7 Service Pack 1 | >= 6.1.0 and < 6.1.7601.25661Vendor says fixed in: not stated | |
| Microsoft Windows 8.1 | >= 6.3.0 and < 6.3.9600.20069Vendor says fixed in: not stated | |
| Microsoft Windows Server 2008 R2 Service Pack 1 | >= 6.1.7601.0 and < 6.1.7601.25661Vendor says fixed in: not stated | |
| Microsoft Windows Server 2012 | >= 6.2.9200.0 and < 6.2.9200.23409Vendor says fixed in: not stated | |
| Microsoft Windows Server 2012 R2 | >= 6.3.9600.0 and < 6.3.9600.20069Vendor says fixed in: not stated | |
| Microsoft Windows Server 2016 | >= 10.0.14393.0 and < 10.0.14393.4530Vendor says fixed in: not stated | |
| Microsoft Windows Server 2019 | >= 10.0.17763.0 and < 10.0.17763.2061Vendor says fixed in: not stated |
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.
Products named in our analysis
- microsoft:windows_10_1507
- microsoft:windows_10_1607
- microsoft:windows_10_1809
- microsoft:windows_10_1909
- microsoft:windows_10_2004
- microsoft:windows_10_20h2
- microsoft:windows_10_21h1
- microsoft:windows_7
- microsoft:windows_8.1
- microsoft:windows_rt_8.1
- microsoft:windows_server_2008
- microsoft:windows_server_2012
- microsoft:windows_server_2016
- microsoft:windows_server_2019
Fix and mitigation
WAF and other mitigations
Can a WAF block it? No. This is an out-of-bounds write, a memory-corruption bug. Generic WAF rules do not recognise the input that triggers it; only a rule written for this specific CVE can, and only if the triggering request has a recognisable shape.
Also consider: patch
Based on the weakness type only; no CVE-specific evidence yet. We check Cloudflare, AWS, Google Cloud Armor and Azure; for Akamai, Imperva, Fastly, F5, ask your vendor.
Remediation steps (AI-written)
Step-by-step remediation is generated for accounts on the Max plan, for CVEs that match a technology in their stack. Add this technology to your stack to see the fix checklist.
Exploitation evidence
- CISA KEV catalog
- Listed since 3 Nov 2021.
- CISA due date
- 17 Nov 2021, the remediation deadline for US federal agencies
- CISA required action
- Apply updates per vendor instructions.
- Public exploit code
- None on record in Exploit-DB, Metasploit, Nuclei templates or PoC-in-GitHub.
- CISA SSVC
- exploitation active, automatable yes, technical impact totalAssessed by CISA 4 Feb 2025 (SSVC 2.0.3). Exploitation is none, poc (public proof of concept) or active.
Timeline
- 16 Jul 2021Published
- 3 Nov 2021Added to CISA KEV (exploited in the wild)109 days (about 4 months) later
- 17 Nov 2021CISA remediation due date (US federal agencies)14 days later
- 4 Feb 2025CISA SSVC assessment: exploitation active1,176 days (about 3 years) later
- 10 Aug 2026CVE record last updated552 days (about 2 years) later
- 12 Nov 2026Analysed by vulneraibility.com94 days (about 3 months) later
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N
| Metric | Value | What it means |
|---|---|---|
| Attack vector | NetworkReachable over the internet or any routable network. | Reachable over the internet or any routable network. |
| Attack complexity | HighNeeds specific conditions, a race or a particular configuration. | Needs specific conditions, a race or a particular configuration. |
| Privileges required | NoneThe attacker needs no prior access. | The attacker needs no prior access. |
| User interaction | RequiredA victim must click, open or otherwise cooperate. | A victim must click, open or otherwise cooperate. |
| Scope | UnchangedImpact stays within the vulnerable component. | Impact stays within the vulnerable component. |
| Confidentiality | HighTotal data disclosure possible. | Total data disclosure possible. |
| Integrity | HighComplete modification possible. | Complete modification possible. |
| Availability | NoneThe service stays up. | The service stays up. |
Common questions
Is CVE-2021-34448 being exploited?
Yes. CVE-2021-34448 appears in CISA's Known Exploited Vulnerabilities catalog, which means exploitation in the wild has been confirmed and reported. Treat it as active rather than theoretical, and patch it ahead of higher-scoring vulnerabilities that carry no exploitation evidence.
How severe is CVE-2021-34448?
CVE-2021-34448 is rated Medium with a CVSS score of 6.8. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2021-34448?
Yes. A fix has been recorded for CVE-2021-34448. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2021-34448 affect?
CVE-2021-34448 affects microsoft:windows_10_1507, microsoft:windows_10_1607, microsoft:windows_10_1809, microsoft:windows_10_1909, and 10 further products or versions. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
References
3 references in the CVE record, grouped by the tags the record gives them.
Patches (1)
- msrc.microsoft.com /update-guide/vulnerability/CVE-2021-34448
Other links (2)
- portal.msrc.microsoft.com /en-US/security-guidance/advisory/CVE-2021-34448
- cisa.gov /known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-34448
Where the data on this page comes from
- CVE List (CVE.org): description, affected versions, references; CVE Terms of Use
- NVD: CVSS and CPE data
- CISA KEV catalog: exploitation, date added, due date
- CISA Vulnrichment (ADP): SSVC decision points
- FIRST EPSS: exploit probability and percentile
Summary, impact and triage tags: written by our AI analysis pipeline from the sources above. Check them against the sources.
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