# CVE-2021-27878 — Veritas Backup Exec **CISA KEV** · **Ransomware** > As of 2025-10-21, CVE-2021-27878 is a HIGH-severity vulnerability in Veritas Backup Exec, CVSS v3.1 8.8, EPSS 23.9% (97.6th 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-2021-27878, 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-2021-27878? An issue was discovered in Veritas Backup Exec before 21.2. The communication between a client and an Agent requires successful authentication, which is typically completed over a secure TLS communication. However, due to a vulnerability in the SHA Authentication scheme, an attacker is able to gain unauthorized access and complete the authentication process. Subsequently, the client can execute data management protocol commands on the authenticated connection. The attacker could use one of these commands to execute an arbitrary command on the system using system privileges. Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs low-privilege credentials, needs no user interaction, and has high impact on confidentiality, integrity, availability. 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:** 8.8 — HIGH (`CVSS:3.1/AC:L/AV:N/A:H/C:H/I:H/PR:L/S:U/UI:N`) - **EPSS (FIRST):** 23.9% probability of exploitation in the next 30 days, higher than 97.6% 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-2021-27878 being exploited? CISA added CVE-2021-27878 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-2021-27878 is publicly available. 1 public proof-of-concept repository is tracked for this identifier. It currently carries a trending score of 42 in the Threadlinqs vulnerability feed. - [trickest/cve](https://github.com/trickest/cve/blob/main/2021/CVE-2021-27878.md) (trickest) ## Affected products and versions - **Veritas**: Backup Exec ## How to fix CVE-2021-27878 Vendor advisory: [https://www.veritas.com/content/support/en_US/security/VTS21-001#issue3](https://www.veritas.com/content/support/en_US/security/VTS21-001#issue3). Because CVE-2021-27878 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-2021-27878 1 tracked threat in the Threadlinqs corpus references CVE-2021-27878, either in the campaign’s CVE list or as an indicator on the campaign record. - [BlackCat/ALPHV Ransomware Abuses Azure Storage Account Keys via Sphynx Encryptor to Mass-Encrypt Cloud Storage](https://intel.threadlinqs.com/threat/TL-2026-1712) — HIGH · 2026-07-26 ## Sources Enriched from CVE.org, NVD, FIRST EPSS, CISA KEV, GitHub Security Advisories, public proof-of-concept repositories. Last verified by Threadlinqs on 2026-07-27. This product uses the NVD API but is not endorsed or certified by the NVD. **Other references** - [veritas.com](https://www.veritas.com/content/support/en_US/security/VTS21-001#issue3) - [packetstormsecurity.com](http://packetstormsecurity.com/files/168506/Veritas-Backup-Exec-Agent-Remote-Code-Execution.html) Canonical: https://intel.threadlinqs.com/cve/CVE-2021-27878 Full detection coverage and IOCs for threats exploiting CVE-2021-27878 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp