How severe is CVE-2021-36159?

CVE-2021-36159 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity none, and availability high.

Is CVE-2021-36159 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (84th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-36159?

CVE-2021-36159 affects Freebsd Libfetch. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-36159?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2021-36159 published?

CVE-2021-36159 was published on 2021-08-03 and last updated on 2026-06-17.

CVE-2021-36159

CVE-2021-36159 is a critical-severity vulnerability in Freebsd Libfetch with a CVSS 3.x base score of 9.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-125.

Key facts

Severity: Critical (CVSS 3.x base score 9.1)
CVSS v2: 6.4
EPSS exploit prediction: 3% (84th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-125
Affected product: Freebsd Libfetch
Published: 2021-08-03
Last modified: 2026-06-17

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.

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.
How severe is CVE-2021-36159?: CVE-2021-36159 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity none, and availability high.
Is CVE-2021-36159 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (84th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-36159?: CVE-2021-36159 affects Freebsd Libfetch. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-36159?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2021-36159 published?: CVE-2021-36159 was published on 2021-08-03 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:freebsd:libfetch:*:*:*:*:*:*:*:*

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