Threat Intelligence / CVE / CVE-2021-27877

CVE-2021-27877 — Veritas Backup Exec

CISA KEVRansomware
CVSS v3.1 8.2 (HIGH) · EPSS 64.9% (higher than 99.1% of all scored CVEs) · Priority 10/10 · Published 2021-03-01

As of 2025-10-21, CVE-2021-27877 is a HIGH-severity vulnerability in Veritas Backup Exec, CVSS v3.1 8.2, EPSS 64.9% (99.1th percentile). It is listed in the CISA Known Exploited Vulnerabilities catalog (added 2023-04-07), with a US federal remediation deadline of 2023-04-28, and CISA links it to known ransomware campaigns. Threadlinqs Intelligence links 1 tracked threat campaign to CVE-2021-27877, most recently “BlackCat/ALPHV Ransomware Abuses Azure Storage Account Keys via Sphynx Encryptor to Mass-Encrypt Cloud Storage”.

Last updated: 2025-10-21

What is CVE-2021-27877?

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.

Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs no user interaction, and has high impact on confidentiality. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 2022 days ago.

Severity and exploitation probability

CVSS v3.1 base score
8.2 — HIGH
CVSS:3.1/AC:L/AV:N/A:N/C:H/I:L/PR:N/S:U/UI:N
EPSS (FIRST)
64.9% probability of exploitation in the next 30 days, higher than 99.1% of all scored CVEs
CISA KEV
Listed since 2023-04-07, federal remediation deadline 2023-04-28 — used in known ransomware campaigns
Threadlinqs priority
10/10 — CISA lists it as used in ransomware, which Threadlinqs scores at the maximum
Published
2021-03-01, last modified 2025-10-21

Is CVE-2021-27877 being exploited?

CISA added CVE-2021-27877 to the Known Exploited Vulnerabilities catalog on 2023-04-07, which means the agency holds evidence of exploitation in the wild; US federal civilian agencies had to remediate it by 2023-04-28 under BOD 22-01. CISA flags the vulnerability as one used in known ransomware campaigns. Weaponised exploit code for CVE-2021-27877 is publicly available. 2 public proof-of-concept repositories are tracked for this identifier. A ProjectDiscovery Nuclei detection template exists (javascript/cves/2021/CVE-2021-27877.yaml). It currently carries a trending score of 45 in the Threadlinqs vulnerability feed.

Affected products and versions

How to fix CVE-2021-27877

Vendor advisory: https://www.veritas.com/content/support/en_US/security/VTS21-001#issue1. Because CVE-2021-27877 is KEV-listed, US federal civilian agencies were required to apply the vendor fix, or stop using the product, by 2023-04-28. Apply the vendor fix referenced above to every affected product listed in this record, then confirm the running version against the vendor advisory.

Threat activity tracking CVE-2021-27877

1 tracked threat in the Threadlinqs corpus references CVE-2021-27877, either in the campaign’s CVE list or as an indicator on the campaign record.

Sources

Enriched from CVE.org, NVD, FIRST EPSS, CISA KEV, GitHub Security Advisories, public proof-of-concept repositories, ProjectDiscovery Nuclei. Last verified by Threadlinqs on . This product uses the NVD API but is not endorsed or certified by the NVD.

Other references

Full detection coverage & IOCs for threats exploiting CVE-2021-27877 are available via the Threadlinqs MCP server (Purple tier). View plans →

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