CVE-2021-33558
Published: April 11, 2026
Official Description
Boa 0.94.13 allows remote attackers to obtain sensitive information via a misconfiguration involving backup.html, preview.html, js/log.js, log.html, email.html, online-users.html, and config.js. NOTE: multiple third parties report that this is a site-specific issue because those files are not part of Boa.
Risk Analysis
This vulnerability in Boa 0.94.13 allows remote attackers to obtain sensitive information due to a misconfiguration involving specific files. While some reports suggest this is a site-specific issue, its presence in CISA's KEV catalog indicates it has been actively exploited.
This vulnerability is actively exploited in the wild. Attackers can remotely obtain sensitive information due to the misconfiguration.
Review and secure the configuration of Boa 0.94.13 web servers, ensuring that sensitive files are not publicly accessible. Remove or restrict access to files like backup.html, preview.html, js/log.js, log.html, email.html, online-users.html, and config.js if they are not intended for public viewing.
Technical Analysis
CVE-2021-33558 requires local access, meaning attackers must already have a foothold on the target system.
Exploitation requires some privileges, which limits the exposure to scenarios where an attacker has already gained initial access.
CISA has added CVE-2021-33558 to the Known Exploited Vulnerabilities (KEV) catalog, confirming active exploitation in the wild. U.S. federal agencies are required to patch this within the mandated timeframe, and all organizations should treat remediation as urgent.
Exploit & PoC Resources
Quick Facts
Recommended Actions
- →Apply vendor patches immediately
- →Monitor CVE-2021-33558 in threat intel feeds
- →Review IDS/IPS signatures for exploitation attempts
- !CISA KEV: Federal agencies must patch per BOD 22-01 timeline
- !Active exploitation confirmed — treat as P1