Privilege escalation via opaque key blob overflow
Published Jun 8, 2021 · Updated Oct 21, 2025
An out-of-bounds write in Microsoft Enhanced Cryptographic Provider allows local users to elevate privileges through a crafted key blob. rsaenh.dll's ImportOpaqueBlob calculates an allocation size from unchecked 32-bit length fields, permits integer wraparound, then copies a larger attacker-controlled field into the undersized buffer. Exploitation requires existing local code execution; demonstrated attacks escaped an Adobe Reader sandbox and ran code with the broker process's privileges.
Summary
What happened
An out-of-bounds write in Microsoft Enhanced Cryptographic Provider allows local users to elevate privileges through a crafted key blob. rsaenh.dll's ImportOpaqueBlob calculates an allocation size from unchecked 32-bit length fields, permits integer wraparound, then copies a larger attacker-controlled field into the undersized buffer. Exploitation requires existing local code execution; demonstrated attacks escaped an Adobe Reader sandbox and ran code with the broker process's privileges.
The record
- CVE
- CVE-2021-31199
- Published
- Jun 8, 2021
- Updated
- Oct 21, 2025
- Vendor
- Microsoft
- Product
- Windows 10 Version 1507
- Classifications
- T1068
- Attack vector
- local
- Privileges
- authenticated
Timeline
How it unfolded
- Jun 8, 2021CVE publishedPublication date reported by the CVE source.
- Nov 3, 2021Exploitation reportedCISA Known Exploited Vulnerabilities listing
- Oct 21, 2025Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=10.0.0 <10.0.10240.18967
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Escaping Adobe Sandbox CVE-2021-31199 exploit analysisfunctional · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Reported exploitation
- CISA Known Exploited Vulnerabilities listingknown exploited catalog
- KNOTWEED Subzero exploit chainexploit chain
Technologies
Your stack
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Your stack
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