CVE-2019-18928 – CVE-2019-18928 is an authentication bypass vuln... (How to Fix)

Q: What is the severity of CVE-2019-18928?

CVE-2019-18928 has a CVSS score of 9.8 (CRITICAL). CVE-2019-18928 is an authentication bypass vulnerability in Cyrus IMAP where HTTP requests on the same connection can inherit authentication context from previous unrelated requests, allowing privilege escalation. This affects Cyrus IMAP versions 2.5.x before 2.5.14 and 3.x before 3.0.12. Attackers can potentially gain unauthorized access to email accounts or administrative functions.

📋 TL;DR

CVE-2019-18928 is an authentication bypass vulnerability in Cyrus IMAP where HTTP requests on the same connection can inherit authentication context from previous unrelated requests, allowing privilege escalation. This affects Cyrus IMAP versions 2.5.x before 2.5.14 and 3.x before 3.0.12. Attackers can potentially gain unauthorized access to email accounts or administrative functions.

💻 Affected Systems

Products:

Cyrus IMAP

Versions: 2.5.x before 2.5.14, 3.x before 3.0.12

Operating Systems: Linux, Unix-like systems

Default Config Vulnerable: ⚠️ Yes

Notes: Affects both HTTP and potentially other connection-based authentication mechanisms in Cyrus IMAP.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Full system compromise where an attacker gains administrative privileges, accesses all email accounts, and potentially executes arbitrary code on the server.

🟠

Likely Case

Unauthorized access to user email accounts, privilege escalation from regular user to administrator, or access to other users' mailboxes.

🟢

If Mitigated

Limited impact with proper network segmentation, authentication logging, and intrusion detection systems in place.

🌐 Internet-Facing: HIGH

🏢 Internal Only: MEDIUM

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Requires ability to establish and maintain HTTP connections to the Cyrus IMAP server. The vulnerability involves session/connection state manipulation.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: 2.5.14 for 2.5.x, 3.0.12 for 3.x

Vendor Advisory: https://www.cyrusimap.org/imap/download/release-notes/

Restart Required: Yes

Instructions:

1. Backup configuration and data. 2. Download patched version from official Cyrus IMAP repository. 3. Stop Cyrus IMAP service. 4. Install updated version. 5. Restart Cyrus IMAP service. 6. Verify service is running correctly.

🔧 Temporary Workarounds

Connection Limiting

linux

Limit concurrent connections per IP address to reduce attack surface

# Configure in cyrus.conf or via firewall rules
# Example iptables: iptables -A INPUT -p tcp --dport 143 -m connlimit --connlimit-above 10 -j REJECT

Network Segmentation

linux

Restrict access to Cyrus IMAP to trusted networks only

# Firewall example: iptables -A INPUT -p tcp --dport 143 -s trusted_network -j ACCEPT
# iptables -A INPUT -p tcp --dport 143 -j DROP

🧯 If You Can't Patch

Implement strict network access controls to limit who can connect to the Cyrus IMAP server
Enable detailed authentication logging and monitor for suspicious authentication patterns

🔍 How to Verify

Check if Vulnerable:

Check Cyrus IMAP version: cyradm --version or examine package version. Vulnerable if version is 2.5.0-2.5.13 or 3.0.0-3.0.11.

Check Version:

cyradm --version 2>&1 | head -1

Verify Fix Applied:

Verify version is 2.5.14 or higher for 2.5.x branch, or 3.0.12 or higher for 3.x branch. Test authentication with multiple concurrent connections.

📡 Detection & Monitoring

Log Indicators:

Multiple authentication attempts from same IP in short timeframe
User accessing mailboxes they shouldn't have permissions for
Authentication context switching in logs

Network Indicators:

Unusual connection patterns to IMAP ports
Multiple HTTP requests over persistent connections with different authentication contexts

SIEM Query:

source="cyrus.log" AND ("authentication failure" OR "permission denied") | stats count by src_ip, user

📊 Metadata

CVE ID: CVE-2019-18928

CVSS v3 Score: 9.8 (CRITICAL)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Published: November 15, 2019

Last Updated: November 21, 2024

🔗 References

https://lists.debian.org/debian-lts-announce/2022/06/msg00013.html Mailing List,Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/LAGKPZDXQ6KRUGQVRAO6N4PCINP6KS5F/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/PHV3TUU53WCKJ3BBRK2EHAF44MSZEFK6/
https://www.cyrusimap.org/imap/download/release-notes/2.5/x/2.5.14.html Patch,Release Notes,Third Party Advisory
https://www.cyrusimap.org/imap/download/release-notes/3.0/x/3.0.12.html Patch,Release Notes,Third Party Advisory
https://lists.debian.org/debian-lts-announce/2022/06/msg00013.html Mailing List,Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/LAGKPZDXQ6KRUGQVRAO6N4PCINP6KS5F/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/PHV3TUU53WCKJ3BBRK2EHAF44MSZEFK6/
https://www.cyrusimap.org/imap/download/release-notes/2.5/x/2.5.14.html Patch,Release Notes,Third Party Advisory
https://www.cyrusimap.org/imap/download/release-notes/3.0/x/3.0.12.html Patch,Release Notes,Third Party Advisory

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