A security researcher has published a second zero-day vulnerability in the Steam gaming client after being banned from Valve's bug bounty program on HackerOne. The researcher had previously reported a similar vulnerability, which Valve initially refused to acknowledge as a security flaw, but eventually patched after public disclosure. The incident has sparked criticism of Valve's handling of bug reports and its decision to exclude elevation of privilege vulnerabilities from its bug bounty program. This has led to concerns about the security of the Steam client and the potential risks to its users.