Overview The Kaltura HTML5 Player Library (mwEmbed / html5lib) contains two vulnerabilities, both involving the same insecure deserialization flaw, that enable arbitrary file read and remote code execution. Affected versions include html5lib v2.45, v2.103 and earlier, and other v2.x releases that expose the vulnerable mwEmbedLoader.php endpoint. Until a vendor patch is available, users are advised to restrict access to the affected endpoint or disable it entirely. Description Kaltura is an AI video platform that provides tools for video management, publishing, playback, and integration with web applications. Kaltura’s HTML5 player library exposes the mwEmbedLoader.php endpoint, which accepts a user-controlled ServiceUrl parameter as the target URL for backend API requests. The KalturaClientBase PHP client library fetches data from this URL and automatically deserializes it using PHP's unserialize() function without validating source, scheme, or content. CVE-2026-19913 results from the combination of this unsafe deserialization flaw and improper error-handling behavior. An attacker can provide the location of a local file to ServiceUrl as a file:// path, and the client will fetch the internal file's contents and attempt to deserialize them. When deserialization fails, the raw bytes are reflected back to the client in the resulting error message, enabling the attacker to read any file accessible to the web-server user. CVE-2026-19912 is caused by insufficient sanitization of the parameter uiconf_id , which is appended to the base cache folder path when the application writes data to disk. Because this value is user-controlled and unsanitized, an attacker can supply values that include directory traversal sequences such as ../ to redirect file writes outside the intended cache directory. When the deployment uses the default file-based cache backend, an attacker can direct ServiceUrl to a malicious serialized object containing executable PHP code, then supply a uiconf_id path value that writes its deserialized fields to a web-accessible directory. The attacker can then request the file directly to achieve remote code execution as the web-server user. A memcache-only backend may suppress the file write and prevent this specific code-execution path, but the underlying unsafe deserialization behavior and unsanitized path construction remain present. Impact These vulnerabilities allow a remote, unauthenticated attacker to read arbitrary local files and execute arbitrary commands as the web-server user. No authentication or Kaltura session token is required to exploit either issue; an attacker only needs network access to the affected html5lib endpoint. CVE-2026-19913 can be abused to obtain database credentials, administrative secrets, API keys, or any other sensitive information hosted on the affected instance. Remote code execution achieved through CVE-2026-19912 allows an attacker to modify or exfiltrate platform data, deploy tools for persistence and lateral movement, and further compromise affected Kaltura deployments. Because the affected endpoint is also exposed on Kaltura's shared, multi-tenant CDN infrastructure, these vulnerabilities affect not only individual customer installations, but also every tenant served by these shared hosts. Solution Unfortunately, the CERT/CC was unable to reach Kaltura to coordinate these vulnerabilities. To reduce risk until a patch is available, users are advised to restrict or disable external access to the mwEmbedLoader.php endpoint, and enforce a strict allow-list for ServiceUrl that only permits known, legitimate backend API URLs. Acknowledgements Thanks to Gerjan Wemekamp (AndDone) for researching and reporting these vulnerabilities. This document was written by Molly Jaconski. Vendor Information One or more vendors are listed for this advisory. Please reference the full report for more information. Other Information CVE IDs: CVE-2026-19912 CVE-2026-19913 Date Public: 2026-08-25 Date First…