CVE-2024-52508: Nextcloud Mail Information Disclosure Flaw

CVE-2024-52508 Overview

CVE-2024-52508 is an information disclosure vulnerability in Nextcloud Mail, the mail application for the Nextcloud self-hosted productivity platform. The flaw arises during mail account setup when the target email domain does not support autoconfiguration. Nextcloud Mail attempts to retrieve configuration data from a predictable autoconfig.<tld> host. If an attacker registers the corresponding autoconfig.tld domain, the user's submitted email address and password are transmitted to the attacker-controlled server. The issue is tracked under [CWE-200] (Exposure of Sensitive Information to an Unauthorized Actor).

Critical Impact

User-supplied mail credentials can be exfiltrated to an attacker-registered domain during account setup, enabling full mailbox compromise.

Affected Products

• Nextcloud Mail versions prior to 1.14.6
• Nextcloud Mail versions prior to 1.15.4, 2.2.11, 3.6.3, and 3.7.7
• Nextcloud Mail versions prior to 4.0.0

Discovery Timeline

• 2024-11-15 - CVE-2024-52508 published to NVD
• 2025-10-01 - Last updated in NVD database

Technical Details for CVE-2024-52508

Vulnerability Analysis

Nextcloud Mail performs an autoconfiguration lookup when users add a new mail account. The client derives candidate configuration endpoints from the email domain, including a host built as autoconfig.<tld>. This lookup pattern strips the second-level domain and queries only the top-level domain segment, producing hostnames such as autoconfig.tld that any third party can register.

When the request reaches the attacker-controlled autoconfig endpoint, the Mail app submits the email address along with the password the user entered during setup. The disclosure occurs before the user has confirmed a trusted server, so no anomaly is visible to the victim. The vulnerability is categorized as Information Disclosure with credential exposure consequences.

Root Cause

The root cause is improper construction of the autoconfiguration target host. The implementation does not constrain the lookup to the full email domain (for example autoconfig.example.tld) and instead permits a fallback that resolves to a registrable parent domain. Combined with transmission of credentials to an unvalidated endpoint, this allows trust to be misplaced in a third-party-owned host.

Attack Vector

Exploitation requires the attacker to register autoconfig.tld for a top-level domain whose users do not publish standard Mozilla or Microsoft autoconfiguration records. When a Nextcloud Mail user enters credentials for any address ending in that TLD, the client posts the address and password to the attacker's web server. No authentication or prior access to the Nextcloud instance is required; user interaction is limited to initiating mail account setup. See the GitHub Security Advisory GHSA-vmhx-hwph-q6mc and HackerOne Report #2508422 for the full technical write-up.

Detection Methods for CVE-2024-52508

Indicators of Compromise

• Outbound HTTPS or HTTP requests from Nextcloud servers to hosts matching the pattern autoconfig.<tld> where <tld> is a bare top-level domain rather than a full organizational domain.
• Mail account setup activity in Nextcloud logs immediately followed by external connections to unfamiliar autoconfig endpoints.
• DNS resolutions for autoconfig.com, autoconfig.net, autoconfig.io, or similar TLD-only hostnames originating from Nextcloud infrastructure.

Detection Strategies

• Inspect Nextcloud Mail application logs for autoconfiguration lookups that resolve to second-level autoconfig.<tld> hosts rather than autoconfig.<domain>.<tld>.
• Correlate web proxy logs with mail account creation events to identify credentials transmitted to non-corporate domains.
• Monitor for the patched commit a84c70e15d814dab6f0e8eda71bbaaf48152079b in deployed Nextcloud Mail builds to confirm remediation status.

Monitoring Recommendations

• Establish an allowlist of known autoconfiguration endpoints (such as Mozilla ISPDB and provider-specific autodiscover URLs) and alert on deviations.
• Track outbound POST requests containing email field patterns from Nextcloud hosts during account onboarding windows.
• Review mailbox login telemetry for accounts onboarded prior to patching for signs of unauthorized access from atypical geolocations.

How to Mitigate CVE-2024-52508

Immediate Actions Required

• Upgrade Nextcloud Mail to version 1.14.6, 1.15.4, 2.2.11, 3.6.3, 3.7.7, or 4.0.0, depending on the branch in use.
• Force password rotation for any mail accounts configured through Nextcloud Mail prior to patching, especially those using TLDs without published autoconfiguration records.
• Audit Nextcloud Mail logs for prior autoconfiguration requests sent to unverified third-party hosts.

Patch Information

The fix is delivered in the Nextcloud Mail commit a84c70e and merged through Pull Request #9964. Administrators should apply the corresponding release across all maintained branches and verify the version in the Nextcloud app management console.

Workarounds

• Restrict outbound network access from Nextcloud servers to a curated list of known autoconfiguration providers until patching is complete.
• Disable the Nextcloud Mail app temporarily for tenants that cannot upgrade immediately.
• Advise users to defer adding new mail accounts until the patched release is deployed.

# Verify installed Nextcloud Mail version and upgrade via occ
sudo -u www-data php occ app:list | grep mail
sudo -u www-data php occ app:update mail
sudo -u www-data php occ app:list | grep mail