How severe is CVE-2021-27877?

CVE-2021-27877 has a CVSS score of 8.2/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-27877?

Affected package information for CVE-2021-27877 is not yet fully mapped. Check the official advisory links for details.

How do I fix CVE-2021-27877?

No fixed version has been published for CVE-2021-27877 yet. Monitor the advisory for updates, apply mitigations recommended by the vendor, and use O3 Security to track when a fix becomes available in your stack.

Is CVE-2021-27877 actively exploited in the wild?

Yes. There are 3 known exploit references for CVE-2021-27877, including 3 in-the-wild exploitations observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-27877?

CVE-2021-27877 has an EPSS (Exploit Prediction Scoring System) score of 40.3%, placing it in the 97th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score warrants monitoring and prompt remediation.

Is CVE-2021-27877 in the CISA Known Exploited Vulnerabilities catalog?

Yes. CVE-2021-27877 (Veritas Backup Exec Agent Improper Authentication Vulnerability) was added to CISA's Known Exploited Vulnerabilities (KEV) catalog on 2023-04-07. CISA required all US federal civilian agencies to remediate this vulnerability by 2023-04-28. The required action was: Apply updates per vendor instructions. This CVE has been used in known ransomware campaigns. Being listed in the KEV catalog is the strongest possible confirmation of active exploitation — treat this as a critical priority.

Which products and versions are affected by CVE-2021-27877?

CVE-2021-27877 affects veritas backup exec. Check the affected-products list on this page against your deployed version to confirm exposure.

When was CVE-2021-27877 published, and has it been updated?

CVE-2021-27877 was published on March 1, 2021 and was last updated on November 3, 2025. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

CISA KEV·Added 2023-04-07 — agencies required to remediate by 2023-04-28 · Ransomware

CVE-2021-27877

HIGH

An issue was discovered in Veritas Backup Exec before 21.2. It supports multiple authentication schemes: SHA authentication is one of these. This authentication scheme is no longer…

Published

Mar 1, 2021

Updated

Nov 3, 2025

Affected

0 pkgs

Patched

None yet

Exploits

3 known

EPSS Exploitation Probability

via FIRST.org ↗

40.3%probability of exploitation in next 30 days

High Risk97th percentile-5.16%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Description

An issue was discovered in Veritas Backup Exec before 21.2. It supports multiple authentication schemes: SHA authentication is one of these. This authentication scheme is no longer used in current versions of the product, but hadn't yet been disabled. An attacker could remotely exploit this scheme to gain unauthorized access to an Agent and execute privileged commands.

Affected Products

1 product · 1 configurations

Application

backup execveritas

< 21.2

range

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

An issue was discovered in Veritas Backup Exec before 21.2. It supports …

github.comMetasploitSep 2022

An issue was discovered in Veritas Backup Exec before 21.2. It supports …

packetstormsecurity.comNVDSep 2022

An issue was discovered in Veritas Backup Exec before 21.2. It supports …

cisa.govCISAApr 2023

Frequently Asked Questions

O3 Security · Impact-Aware SCA

Is CVE-2021-27877 in your stack?

O3 detects CVE-2021-27877 across dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

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