CVE-2021-36159
CVSS v3
9.1
CRITICAL
EPSS Score
2.6 %
exploit probability, as of 2026-09-25
CISA KEV
No
known exploited
Exploitation
—
SSVC status
Description
libfetch before 2021-07-26, as used in apk-tools, xbps, and other products, mishandles numeric strings for the FTP and HTTP protocols. The FTP passive mode implementation allows an out-of-bounds read because strtol is used to parse the relevant numbers into address bytes. It does not check if the line ends prematurely. If it does, the for-loop condition checks for the '\\0' terminator one byte too late.
Technical details
- Published
- 2021-08-03
Frequently asked questions
What is CVE-2021-36159?
libfetch before 2021-07-26, as used in apk-tools, xbps, and other products, mishandles numeric strings for the FTP and HTTP protocols. The FTP passive mode implementation allows an out-of-bounds read because strtol is used to parse the relevant numbers into address bytes. It does not check if the line ends prematurely. If it does, the for-loop condition checks for the '\\0' terminator one byte too late.
Is CVE-2021-36159 actively exploited?
Active exploitation of CVE-2021-36159 has not been confirmed. Its EPSS score was 2.6% on 2026-09-25, the estimated probability of exploitation in the next 30 days.
What is the CVSS score for CVE-2021-36159?
CVE-2021-36159 has a CVSS v3 base score of 9.1 (CRITICAL severity).
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