RCE in Fail2ban
CVE-2021-32749
fail2ban is a daemon to ban hosts that cause multiple authentication errors. In versions 0.9.7 and prior, 0.10.0 through 0.10.6, and 0.11.0 through 0.11.2, there is a vulnerability that leads to possible remote code execution in the mailing action mail-whois. Command `mail` from mailutils package used in mail actions like `mail-whois` can execute command if unescaped sequences (`\n~`) are available in "foreign" input (for instance in whois output). To exploit the vulnerability, an attacker would need to insert malicious characters into the response sent by the whois server, either via a MITM attack or by taking over a whois server. The issue is patched in versions 0.10.7 and 0.11.3. As a workaround, one may avoid the usage of action `mail-whois` or patch the vulnerability manually.
Vulnerability class: Command Injection (OS Command Injection)
EPSS: 0.036 (88.3th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 6.1 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:N/I:H/A:N.
Affected products
- Fail2ban — versions <= 0.9.7, >= 0.10.0, <= 0.10.6, >= 0.11.0, <= 0.11.2
- Fedoraproject Fedora — versions 34, 35
Weakness classification (CWE)
Public proof-of-concept exploits
References
- security-advisories@github.com (Exploit, Patch, Third Party Advisory)
- security-advisories@github.com (Patch, Third Party Advisory)
- security-advisories@github.com (Patch, Third Party Advisory)
- security-advisories@github.com (vendor-advisory)
- security-advisories@github.com (vendor-advisory)
- security-advisories@github.com (vendor-advisory)
Frequently asked questions
- What is CVE-2021-32749?
- CVE-2021-32749 is a medium-severity vulnerability in Fail2ban, classified under OS Command Injection. CVSS score: 6.1/10. Published 2021-07-16.
- How severe is CVE-2021-32749?
- Medium severity. CVSS v3 base score is 6.1 out of 10.
- Is CVE-2021-32749 known to be exploited?
- 2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.