CVE-2018-6882
Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting (XSS) Vulnerability
Description
CVE-2018-6882 is a cross-site scripting (XSS) vulnerability in Synacor Zimbra Collaboration Suite (ZCS), a widely deployed enterprise email and collaboration platform. This vulnerability allows remote attackers to inject arbitrary web scripts or HTML into the application, which are then executed in the context of other users' browser sessions. The cross-site scripting flaw in Zimbra Collaboration Suite can be leveraged to steal session tokens, redirect users to phishing pages, or perform actions on behalf of authenticated users. CISA has added CVE-2018-6882 to the Known Exploited Vulnerabilities catalog with a remediation deadline of May 10, 2022, and the vulnerability is known to be used in ransomware campaigns. The EPSS percentile of approximately 98% indicates a very high probability of exploitation.
KEV Information
CVSS Score
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:NOpen in CalculatorAffected Products
| Vendor | Product | Version |
|---|---|---|
| synacor | zimbra collaboration suite | < 8.7.0; 8.7.0; 8.8.0; 8.8.1; 8.8.2; 8.8.3; 8.8.4; 8.8.5; 8.8.6 |
Multiple CVSS Assessments
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
References
- http://seclists.org/fulldisclosure/2018/Mar/52(Mailing List, Third Party Advisory)
- http://www.securityfocus.com/archive/1/541891/100/0/threaded(Broken Link, Third Party Advisory, VDB Entry)
- https://bugzilla.zimbra.com/show_bug.cgi?id=108786(Broken Link, Issue Tracking, Permissions Required)
- https://wiki.zimbra.com/wiki/Zimbra_Releases/8.8.7(Permissions Required)
- https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories(Vendor Advisory)
- https://www.securify.nl/advisory/SFY20180101/cross-site-scripting-vulnerability-in-zimbra-collaboration-suite-due-to-the-way-it-handles-attachment-links.html(Exploit, Third Party Advisory)
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2018-6882(US Government Resource)
Weakness Type
CWE-79: Improper Neutralization of Input During Web Page Generation (Cross-site Scripting)
The cross-site scripting vulnerability in Zimbra Collaboration Suite occurs when user-supplied input is incorporated into web page output without proper sanitization or encoding. In CVE-2018-6882, the application fails to adequately neutralize malicious input, allowing an attacker to inject JavaScript or HTML that executes in the browser of other authenticated ZCS users, enabling session hijacking, data theft, and unauthorized actions.
Learn more: CWE-79 — Improper Neutralization of Input During Web Page Generation (Cross-site Scripting)
Impact Analysis
CVE-2018-6882 is remotely exploitable over the network and can be triggered without any authentication from the attacker, though user interaction is required for the victim to encounter the injected script, typically through opening a malicious email or clicking a crafted link. The cross-site scripting vulnerability primarily impacts confidentiality by enabling attackers to steal session cookies, authentication tokens, and sensitive email content from authenticated Zimbra users. The integrity of user sessions is compromised as attackers can perform actions on behalf of victims, including reading, sending, and deleting emails, modifying account settings, and forwarding sensitive communications to external addresses. The EPSS percentile of approximately 98% indicates very high exploitation activity, and CISA has confirmed that CVE-2018-6882 is known to be used in ransomware attacks, significantly elevating the threat level for organizations running vulnerable Zimbra deployments.
Exploit Maturity
CISA has confirmed active exploitation of CVE-2018-6882 in the wild by including it in the Known Exploited Vulnerabilities catalog with a remediation deadline of May 10, 2022. The vulnerability is known to be used in ransomware campaigns, indicating that criminal groups are actively leveraging this Zimbra XSS flaw as part of broader attack chains. The EPSS percentile of approximately 98% indicates very high exploitation activity, consistent with the widespread deployment of Zimbra Collaboration Suite in enterprise environments and the ease of exploiting cross-site scripting vulnerabilities. The combination of ransomware association, KEV listing, and high EPSS score makes CVE-2018-6882 an extremely urgent remediation priority.
Remediation
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Update Zimbra Collaboration Suite immediately as directed by CISA: "Apply updates per vendor instructions." Apply the ZCS security patches that address the cross-site scripting vulnerability across all Zimbra servers in your environment.
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Implement Content Security Policy (CSP) headers on the Zimbra web interface to restrict the execution of inline scripts and limit the sources from which scripts can be loaded, providing defense-in-depth against XSS attacks even if the underlying vulnerability is not yet patched.
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Enable HTTP-only and Secure flags on all Zimbra session cookies to prevent JavaScript-based session theft through XSS attacks. Configure the Zimbra server to set the HttpOnly, Secure, and SameSite attributes on authentication cookies.
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Monitor for indicators of XSS exploitation by reviewing Zimbra web server logs for suspicious request patterns containing encoded script tags, unusual URL parameters, and signs of session hijacking such as concurrent sessions from different IP addresses for the same user account.
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Prepare ransomware incident response procedures given the confirmed association of this vulnerability with ransomware campaigns. Ensure email server backups are current and stored offline, implement email-specific monitoring for signs of account compromise such as unexpected forwarding rules, and deploy web application firewall (WAF) rules to filter common XSS payloads targeting Zimbra.
Technical Details
CVE-2018-6882 is a cross-site scripting vulnerability (CWE-79) in Synacor Zimbra Collaboration Suite that results from insufficient input validation and output encoding in the web application's handling of user-supplied data. When the application incorporates user input into HTML responses without proper sanitization, an attacker can inject JavaScript code that executes in the browser context of other authenticated ZCS users. The attack vector is network-based, requiring the victim to interact with the malicious content, such as viewing an email containing the injected script or clicking a crafted link that passes the XSS payload through URL parameters. Once the injected script executes in the victim's browser session, it has full access to the Zimbra web client's DOM, session cookies (if HttpOnly is not set), and can make authenticated API calls to the Zimbra server on behalf of the victim, enabling comprehensive email account compromise.
Frequently Asked Questions
Is CVE-2018-6882 being actively exploited?
Yes, CVE-2018-6882 is being actively exploited in the wild, including in ransomware campaigns. CISA has added this vulnerability to the Known Exploited Vulnerabilities catalog with a remediation deadline of May 10, 2022. The EPSS percentile of approximately 98% confirms very high exploitation activity.
What products are affected by CVE-2018-6882?
CVE-2018-6882 affects Synacor Zimbra Collaboration Suite (ZCS), an enterprise email and collaboration platform. Organizations running vulnerable versions of ZCS should apply patches immediately to address the cross-site scripting vulnerability.
How do I fix CVE-2018-6882?
Apply the Zimbra Collaboration Suite security update that addresses the XSS vulnerability. Implement Content Security Policy headers, enable HttpOnly and Secure flags on session cookies, and deploy a web application firewall with XSS filtering rules as defense-in-depth measures.
How severe is CVE-2018-6882?
CVE-2018-6882 is a high-severity vulnerability with an EPSS percentile of approximately 98% and confirmed use in ransomware attacks. The cross-site scripting flaw enables attackers to hijack Zimbra user sessions, steal email content, and perform unauthorized actions, making it a critical threat to enterprise email security.
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