Today we are issuing security releases of matrix-js-sdk and matrix-react-sdk to patch a pair of High severity vulnerabilities (CVE-2023-28427 / GHSA-mwq8-fjpf-c2gr for matrix-js-sdk and CVE-2023-28103 / GHSA-6g43-88cp-w5gv for matrix-react-sdk).

Affected clients include those which depend on the affected libraries, such as Element Web/Desktop and Cinny. Releases of the affected clients should follow shortly. We advise users of those clients to upgrade at their earliest convenience.

The issues involve prototype pollution via events containing special strings in key locations, which can temporarily disrupt normal functioning of matrix-js-sdk and matrix-react-sdk, potentially impacting the consumer's ability to process data safely.

Although we have only demonstrated a denial-of-service-style impact, we cannot completely rule out the possibility of a more severe impact due to the relatively extensive attack surface. We have therefore classified this as High severity and strongly recommend upgrading as a precautionary measure.

We found these issues during a codebase audit that we had previously announced in an earlier security release of matrix-js-sdk and matrix-react-sdk. The earlier release had already addressed a set of similar vulnerabilities that were assigned CVE-2022-36059 / GHSA-rfv9-x7hh-xc32 and CVE-2022-36060 / GHSA-2x9c-qwgf-94xr, which we had initially decided not to disclose until the completion of the audit. Now that the audit is finished, we are disclosing those previous advisories as well.

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