CVE-2025-31126 Overview
CVE-2025-31126 affects Element X iOS, a Matrix client for iOS developed by Element. The vulnerability exists in versions between 1.6.13 and 25.03.7. Under certain conditions, the entity controlling the element.json well-known file can gain access to the media encryption keys used during an Element Call session. This constitutes an information disclosure weakness classified under [CWE-200]. Element released a fix in version 25.03.8. The issue is exploitable over the network without authentication or user interaction, but impact is limited to confidentiality of call media keys.
Critical Impact
An attacker controlling the element.json well-known configuration file can retrieve media encryption keys for Element Call sessions, undermining the confidentiality of encrypted calls.
Affected Products
- Element X iOS version 1.6.13 through 25.03.7
- Matrix clients relying on Element Call for encrypted voice and video
- Deployments referencing attacker-influenced element.json well-known files
Discovery Timeline
- 2025-04-03 - CVE-2025-31126 published to the National Vulnerability Database (NVD)
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-31126
Vulnerability Analysis
Element X iOS retrieves configuration data from the element.json well-known file to determine service endpoints for features such as Element Call. When the client trusts values delivered through this file without sufficient validation, the party hosting or controlling that file can influence the media key exchange path. Under specific conditions, this influence allows the controlling entity to observe or obtain the media encryption keys negotiated for an Element Call session. Because Element Call relies on these keys to protect real-time audio and video streams, key exposure enables decryption of call media by an unauthorized party. The weakness is scoped to confidentiality; integrity and availability of the call session are not directly affected.
Root Cause
The root cause is improper trust in configuration retrieved from the element.json well-known file. Element X iOS versions 1.6.13 through 25.03.7 accept media-related configuration from this source in a manner that allows the file's controller to intercept or reconstruct call media keys. This maps to [CWE-200] Exposure of Sensitive Information to an Unauthorized Actor.
Attack Vector
Exploitation requires the attacker to control the element.json well-known file referenced by a targeted Element X iOS client. This may occur through compromise of the hosting server, DNS manipulation, or configuration errors that point clients at attacker-controlled infrastructure. Once controlling the file, the attacker can influence Element Call setup so that media encryption keys become accessible. No user interaction beyond initiating or joining a call is required. Refer to the GitHub Security Advisory GHSA-69qf-p24v-rf8j for further technical context.
Detection Methods for CVE-2025-31126
Indicators of Compromise
- Unexpected changes to the element.json well-known file served by a Matrix homeserver domain.
- DNS record modifications redirecting well-known lookups to unfamiliar hosts.
- Element X iOS clients reporting installed versions between 1.6.13 and 25.03.7.
Detection Strategies
- Monitor HTTP responses for /.well-known/element.json and alert on content or hosting changes.
- Compare deployed Element X iOS client versions against the fixed release 25.03.8 during mobile device inventory scans.
- Correlate Element Call session initiations with recent well-known file modifications to identify suspicious call setups.
Monitoring Recommendations
- Enable integrity monitoring on web servers hosting element.json and log all write operations.
- Track DNS changes for domains serving Matrix well-known endpoints and alert on unauthorized updates.
- Review TLS certificate issuance events for well-known hosts to detect impersonation attempts.
How to Mitigate CVE-2025-31126
Immediate Actions Required
- Upgrade all Element X iOS installations to version 25.03.8 or later through the App Store.
- Audit the hosting environment and access controls for any element.json well-known files under organizational control.
- Rotate or invalidate credentials for systems that manage the well-known file if unauthorized access is suspected.
Patch Information
Element addressed CVE-2025-31126 in Element X iOS version 25.03.8. Details are published in the GitHub Security Advisory GHSA-69qf-p24v-rf8j and tracked in GitHub Issue #2441. Users should update through the standard iOS application update channel.
Workarounds
- Restrict write access to the server hosting element.json to a minimal set of administrators.
- Serve the well-known file over TLS with certificate pinning where feasible and enforce HTTP Strict Transport Security (HSTS).
- Advise users to avoid Element Call sessions on unpatched Element X iOS versions until upgrades are completed.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
