Cve20207796 Zimbra Collaboration | Suite Full

The core of CVE-2020-7796 lies in the improper validation of user input within the "mboximport" functionality.

Zimbra includes a feature designed for importing mailbox data (typically used for migrations or backups). The vulnerability exists because the component responsible for handling these imports failed to adequately sanitize file extensions and content types during the upload process.

CVE-2020-27996 serves as a textbook case of how seemingly minor coding oversights—lack of authentication on an internal servlet, combined with poor input validation—can lead to total system compromise. The "full" in its description is no exaggeration: unauthenticated attackers gained root-equivalent code execution on hundreds of thousands of enterprise mail servers. cve20207796 zimbra collaboration suite full

For defenders, the key takeaways are:

As of today, Zimbra has fixed this issue, but scanning data shows that as of late 2022, over 8,000 Zimbra servers remained vulnerable to CVE-2020-27996. If you are running an older Zimbra instance, stop reading—and start patching. The core of CVE-2020-7796 lies in the improper

The following versions of Zimbra Collaboration Suite are vulnerable:

Unlike many vulnerabilities that yield limited access (e.g., file read only, or authenticated RCE), CVE-2020-27996 allows an unauthenticated remote attacker to execute arbitrary system commands with the privileges of the Zimbra service user (typically zimbra). This is the equivalent of handing over the keys to the kingdom. As of today, Zimbra has fixed this issue,

The vulnerability exists within the unrar utility bundled with ZCS. Zimbra uses Amavis to scan email attachments for viruses and spam. Amavis calls external binaries, including unrar, to process archived files (specifically .rar files).

The specific flaw is a buffer overflow vulnerability. The version of unrar included in ZCS did not properly validate the length of user-supplied data before copying it into a fixed-length memory buffer. By crafting a malicious RAR archive with specially designed metadata or content, an attacker can trigger the buffer overflow, overwrite memory, and execute arbitrary shellcode.

| Attribute | Details | |-----------|---------| | CVE ID | CVE-2020-27996 | | Affected Product | Zimbra Collaboration Suite (ZCS) | | Affected Versions | 8.8.15 prior to Patch 11, 9.0.0 prior to Patch 5 | | Component | Proxy Servlet / UserServlet | | Attack Vector | Network / HTTP | | Authentication | None required (Pre-auth RCE) | | CVSS v3 Score | 9.8 (Critical) | | Disclosure Date | November 2020 | | Exploit Maturity | Public PoC available within days of patch |

CVE-2020-27996 is a critical security vulnerability affecting Zimbra Collaboration Suite (ZCS) , specifically versions prior to 8.8.15 Patch 12 and 9.0.0 Patch 4. It is classified as an unauthenticated, remote cross-site scripting (XSS) vulnerability that, when chained with other weaknesses, leads to full mailbox compromise and potential server takeover.