Process crash via stale awk field pointer
Published Nov 15, 2021 · Updated Nov 3, 2025
Use-after-free in BusyBox awk 1.28 through 1.33.1 allows attackers to crash the process or possibly execute code with a crafted pattern. Recursive expression evaluation can reallocate the Fields array while evaluate retains an L.v pointer into its former allocation, which clrvar later dereferences. An attacker must control the awk program argument; a process crash is demonstrated, while code execution remains unproven.
Summary
What happened
Use-after-free in BusyBox awk 1.28 through 1.33.1 allows attackers to crash the process or possibly execute code with a crafted pattern. Recursive expression evaluation can reallocate the Fields array while evaluate retains an L.v pointer into its former allocation, which clrvar later dereferences. An attacker must control the awk program argument; a process crash is demonstrated, while code execution remains unproven.
The record
- CVE
- CVE-2021-42380
- Published
- Nov 15, 2021
- Updated
- Nov 3, 2025
- Vendor
- BusyBox
- Product
- BusyBox
- Classifications
- CWE-416
- Attack vector
- network
- Privileges
- admin
Timeline
How it unfolded
- Nov 15, 2021CVE publishedPublication date reported by the CVE source.
- Nov 3, 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 <1.34.0
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.
Weakness, pattern, technique
Public exploit references
- BusyBox awk assign-while-assign regression caseproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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