Valve’s October 2, 2025 Steam client update added a safeguard that blocks a game launch through Steam when the client detects an attempt to exploit Unity vulnerability CVE-2025-59489. It is a client-side mitigation, not a patch for every affected game. Unity separately made fixes available for affected Editor versions.
What did the October Steam client update change?
Valve’s October 2, 2025 release notes say Steam added “mitigations for Unity CVE-2025-59489, blocking a game launch through the Steam Client when an exploit attempt is detected.” The stated action is conditional: Steam blocks a launch when it detects an exploit attempt. Valve’s notes do not say the client update patches affected games or replaces remediation by their developers.
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Other changes in the release
- An end-of-life alert for 32-bit Windows.
- A fix for backslash characters appearing in some news posts.
- CTRL+TAB support for switching tabs in the tabbed browser.
- Fixes involving the “Mark as private” game setting.
- Support for adding large numbers of non-Steam games to a collection.
Valve’s announcement said Steam Client support for Windows 10 32-bit would end on January 1, 2026, at 10 a.m. That deadline has passed. The same announcement said Steam would continue to run on Windows 10 64-bit and that 32-bit games would remain supported.
What is Unity CVE-2025-59489?
Unity’s security advisory says applications built using affected Unity Editor versions are susceptible to unsafe file loading and local file inclusion. Depending on the operating system, those issues could allow local code execution or information disclosure at the privilege level of the vulnerable application.
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The advisory lists June 4, 2025, as the discovery date and October 2, 2025, as the date a patch became available. It credits RyotaK of GMO Flatt Security Inc. as the discoverer. Unity also stated: “There is no evidence of any exploitation of the vulnerability nor has there been any impact on users or customers.” That is Unity’s report in the advisory; it does not establish that exploitation was impossible.
How Steam’s mitigation differs from Unity’s fixes
| Measure | Who it applies to | Where it intervenes | What to consult |
|---|---|---|---|
| Steam client mitigation | Steam users launching a game when an exploit attempt is detected | At game launch through the Steam Client | Valve’s dated release notes |
| Unity remediation | Developers maintaining projects built with affected Unity Editor versions | In the Editor version and resulting application build | Unity’s advisory and affected/fixed version information |
Unity’s release notes for Unity 6000.0.58f2 list “Scripting: Addressed CVE-2025-59489.” That is one documented fixed release, not a universal version recommendation: developers should check the advisory’s full affected and fixed version tables for their project and platform.
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- This Visa Virtual eGift Card is non-reloadable. No cash or ATM access. Visa Virtual eGift Cards are emailed active.
- Funds do not expire but your Visa Virtual eGift Card has a ‘valid thru’ date (9 years from date of purchase). If funds remain after this date has passed, please call the Toll Free number found on your Visa Virtual eGift Card for a replacement card. A one-time purchase fee applies at the time of checkout.
- This item is not eligible for refund, resale, or return. Available for sale within the United States only. Not available to residents of Puerto Rico, Hawaii, New Mexico, South Dakota, West Virginia and the US Virgin Islands.
What should players and developers do?
For players
Valve’s announcement describes Steam’s mitigation as part of the client update. It does not call for buying additional security software or hardware, and it does not provide a way for players to patch a game built with a vulnerable Unity Editor. If Steam blocks a launch, the release notes do not provide a game-specific workaround; the relevant remediation depends on the game’s developer.
For developers
Use Unity’s advisory to identify whether the Editor version used for a project is affected and which fixed version applies. Rebuild or otherwise remediate affected applications according to Unity’s project- and platform-specific guidance. Do not infer that Unity 6000.0.58f2 is the right target for every project solely because its release notes mention this CVE.
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- Funds do not expire but your Visa Virtual eGift Card has a ‘valid thru’ date (9 years from date of purchase). If funds remain after this date has passed, please call the Toll Free number found on your Visa Virtual eGift Card for a replacement card. A one-time purchase fee applies at the time of checkout.
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