CVE-2026-53704 Overview
CVE-2026-53704 is an out-of-bounds read vulnerability [CWE-125] in the RealMedia demuxer shipped with the GStreamer gst-plugins-ugly package. The demuxer mishandles the FILEINFO metadata section of RealMedia files, parsing variable-name and variable-value pairs through re_skip_pascal_string() without verifying that offsets remain inside the mapped buffer. The loop element count is also read from attacker-controlled data without validation, enabling an infinite loop condition. A crafted RealMedia file can crash or hang the application and may expose limited adjacent memory contents.
Critical Impact
Processing a malicious RealMedia file can cause denial of service through application crash or hang, and may disclose small portions of adjacent process memory.
Affected Products
- GStreamer gst-plugins-ugly package — RealMedia demuxer element
- Linux distributions packaging the affected plugin set (see Red Hat advisory)
- Applications and media frameworks that load the GStreamer RealMedia demuxer
Discovery Timeline
- 2026-06-15 - CVE-2026-53704 published to the National Vulnerability Database (NVD)
- 2026-06-17 - Last updated in the NVD database
Technical Details for CVE-2026-53704
Vulnerability Analysis
The defect resides in the RealMedia demuxer code path that parses the FILEINFO metadata atom. When the demuxer encounters this section, it iterates over a list of variable-name and variable-value Pascal-style strings using the helper re_skip_pascal_string(). This helper advances a read offset based on length prefixes embedded in the file. The demuxer does not check that the advancing offset stays within the bounds of the mapped media buffer.
A second defect compounds the issue. The loop counter that controls how many variable pairs to parse is read directly from the file, with no upper bound or sanity check. An attacker can supply a counter large enough to keep the parser running indefinitely or to drive the read offset past valid memory. The result is a crash, a hang, or a limited information disclosure through reads of memory adjacent to the buffer.
Exploitation requires user interaction: a victim must open or preview a crafted RealMedia file in an application that uses GStreamer. The flaw is reachable over the network because such files can be delivered through web pages, email attachments, or shared media.
Root Cause
The root cause is missing input validation in the RealMedia demuxer. The parser trusts both the length prefixes consumed by re_skip_pascal_string() and the element count that bounds the parsing loop. Neither value is checked against the actual size of the mapped buffer, so attacker-controlled fields drive memory access decisions directly.
Attack Vector
An attacker crafts a RealMedia (.rm, .rmvb) file containing a malformed FILEINFO section. The file is delivered to the target through any channel that triggers media parsing: a browser using a GStreamer-backed pipeline, a desktop media player, a thumbnailer, or an indexing service. When the target processes the file, the demuxer reads past the buffer or enters an infinite loop. See the Red Hat CVE-2026-53704 Advisory and Red Hat Bugzilla Entry #2487614 for technical details. No verified public proof-of-concept code is available at the time of writing.
Detection Methods for CVE-2026-53704
Indicators of Compromise
- Unexpected crashes or hangs in processes that load libgstrealmedia or invoke the rmdemux element.
- Media player, thumbnailer, or indexer processes consuming 100% CPU on a single thread while parsing a .rm or .rmvb file.
- Core dumps referencing GStreamer RealMedia demuxer frames during FILEINFO parsing.
Detection Strategies
- Hunt for processes such as totem, gst-launch-1.0, tracker-extract, or browser content processes terminating shortly after opening RealMedia files.
- Inspect file ingestion paths for RealMedia containers with abnormally large declared element counts in the FILEINFO section.
- Correlate application crash telemetry with recent file downloads or email attachments carrying RealMedia MIME types.
Monitoring Recommendations
- Forward application crash and hang events from Linux endpoints into a centralized analytics platform for correlation with file delivery events.
- Monitor mail and web proxies for inbound .rm and .rmvb attachments and downloads from untrusted sources.
- Track CPU utilization anomalies on shared media processing services that use GStreamer pipelines.
How to Mitigate CVE-2026-53704
Immediate Actions Required
- Apply vendor updates for gst-plugins-ugly as soon as your distribution publishes them.
- Restrict the processing of untrusted RealMedia files on servers that perform automated media handling, such as thumbnailers and indexers.
- Filter inbound .rm and .rmvb files at the email gateway and web proxy until patches are deployed.
Patch Information
No fixed version is enumerated in the current NVD record. Track the Red Hat CVE-2026-53704 Advisory and your Linux distribution's security feed for the corresponding gst-plugins-ugly package update.
Workarounds
- Remove or disable the RealMedia demuxer where it is not required, for example by uninstalling gst-plugins-ugly on systems that do not need RealMedia support.
- Block the rmdemux element through GStreamer registry filtering using the GST_PLUGIN_FEATURE_RANK environment variable to set its rank to NONE.
- Sandbox media processing services with seccomp, AppArmor, or SELinux profiles to limit the impact of a crash or memory read.
# Configuration example: demote the RealMedia demuxer so GStreamer pipelines do not select it
export GST_PLUGIN_FEATURE_RANK="rmdemux:NONE,realmedia:NONE"
# Verify the demuxer is no longer ranked for autoplugging
gst-inspect-1.0 rmdemux | grep -i rank
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
