CVE-2021-3999
HIGHDescription
A flaw was found in glibc. An off-by-one buffer overflow and underflow in getcwd() may lead to memory corruption when the size of the buffer is exactly 1. A local attacker who can control the input buffer and size passed to getcwd() in a setuid program could use this flaw to potentially execute arbitrary code and escalate their privileges on the system.
How to fix
This vulnerability affects an unusually large number of packages. The highest-confidence fixes are shown above; the full list is longer. Check the referenced advisories for complete coverage.
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Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Exploit Intelligence
Moderate risk: more likely to be exploited than 53% of all known CVEs.
References
Related Vulnerabilities
Other CWE-193 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2021-3156 | High | 7.8 | 100% | KEV | Fix |
| CVE-2003-0466 | Critical | 9.8 | 78% | - | - |
| CVE-2023-44444 | High | 7.8 | 56% | - | Fix |
| CVE-2021-23017 | High | 7.7 | 53% | - | Fix |
| CVE-2023-28709 | High | 7.5 | 48% | - | Fix |
| CVE-2018-8828 | Critical | 9.8 | 30% | - | Fix |
Common questions
How do I fix CVE-2021-3999?
Published advisories record a fix for 205 affected products. The "How to fix" section on this page lists the fixed version and source advisory for each one, so apply the entry matching what you actually run.
Is CVE-2021-3999 being actively exploited?
Not that we know of. CVE-2021-3999 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.75% is the estimated probability that it will be exploited in the next 30 days. That is higher than 53% of all scored CVEs.
How severe is CVE-2021-3999?
CVE-2021-3999 has a CVSS v3 base score of 7.8, rated high. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2021-3999 affect?
Published advisories record a fix for glibc (Amazon), glibc-all-langpacks (Amazon), glibc-benchtests (Amazon), glibc-common (Amazon), and 201 more. Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-06-17.