SYSTEM privilege escalation via unchecked string capacity
Published Apr 15, 2020 · Updated Oct 21, 2025
Heap buffer overflow in Microsoft Windows CSRSS allows local users to execute code with SYSTEM privileges through a crafted IPC message. BaseSrvSxsCreateActivationContext validates a UNICODE_STRING against Length but not MaximumLength, which is later trusted when memcpy writes an application name. Any process can reach the handler through ALPC; successful corruption provides a write-what-where primitive for elevated code execution.
Summary
What happened
Heap buffer overflow in Microsoft Windows CSRSS allows local users to execute code with SYSTEM privileges through a crafted IPC message. BaseSrvSxsCreateActivationContext validates a UNICODE_STRING against Length but not MaximumLength, which is later trusted when memcpy writes an application name. Any process can reach the handler through ALPC; successful corruption provides a write-what-where primitive for elevated code execution.
The record
- CVE
- CVE-2020-1027
- Published
- Apr 15, 2020
- Updated
- Oct 21, 2025
- Vendor
- Microsoft
- Product
- Windows 10 Version 1909
- Classifications
- CWE-787, T1068
- Attack vector
- local
- Privileges
- authenticated
Timeline
How it unfolded
- Apr 15, 2020CVE publishedPublication date reported by the CVE source.
- May 23, 2022Exploitation reportedCISA Known Exploited Vulnerabilities catalog 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=unspecified
What conditions does exploitation require?
What is affected?
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.
Public exploit references
- Google Project Zero CSRSS heap-overflow proof of conceptproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Reported exploitation
- CISA Known Exploited Vulnerabilities catalog listingknown exploited catalog
- Chrome sandbox-escape exploit chainexploit chain
Technologies
Your stack
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Your stack
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