CVE-2026-111044 in Sunshine
Summary
by MITRE • 10/17/2026
Sunshine is a self-hosted game stream host for Moonlight. From 2026.329.165800 until 2026.906.222525, Sunshine accepted any client certificate that chained to a stored paired-client certificate, but it did not require the presented certificate to be the exact enabled paired identity. Certificate text was also compared without canonicalizing equivalent PEM encodings. A previously paired client that retains its private key can present an alternate certificate derived from its paired certificate and bypass the Disable control. Equivalent PEM encodings could also cause inconsistent client identity handling. A client that was never paired cannot use this issue, and removing the paired client removes its trust relationship. This issue is fixed in version 2026.906.222525.
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Analysis
by VulDB Data Team • 10/17/2026
The vulnerability identified within Sunshine versions ranging from 2026.329.165800 to 2026.906.222525 represents a critical flaw in the mutual Transport Layer Security authentication logic used for client pairing. As a self-hosted game stream host designed for compatibility with Moonlight, Sunshine relies on certificate-based identity verification to ensure that only authorized devices can establish streaming sessions. The core technical deficiency lies in the validation of presented X.509 certificates during the handshake process. Specifically, the implementation accepted any client certificate that formed a valid chain back to a stored paired-client certificate root or intermediate authority, rather than requiring the presented certificate to be an exact match for the specific identity previously authorized and enabled by the administrator. This relaxation of strict identity binding allows for significant authentication bypass scenarios where the system fails to distinguish between distinct cryptographic identities derived from the same trust anchor.
From a technical perspective, this flaw enables two primary attack vectors related to credential reuse and encoding manipulation. First, any client that was previously paired with the Sunshine host but has since been disabled or removed from active use can still authenticate if it retains its private key. By presenting an alternate certificate derived from its original paired certificate structure, such a legacy device can bypass disable controls effectively reactivating itself without administrative intervention. Second, the vulnerability extends to inconsistencies in PEM encoding handling. The software compared certificate text strings directly without canonicalizing equivalent PEM encodings first. Since X.509 certificates encoded in Privacy-Enhanced Mail format allow for variations in whitespace, line breaks, and header formatting that do not alter the underlying binary data or cryptographic identity, this lack of normalization leads to inconsistent client identity resolution. An attacker could potentially exploit these encoding discrepancies to confuse the validation logic, further undermining the integrity of the authentication process.
The operational impact of this vulnerability is substantial for users relying on Sunshine for secure remote gaming sessions. The primary consequence is a loss of access control granularity. Administrators who have explicitly disabled specific paired clients or removed them from their trusted list cannot guarantee that those devices are truly disconnected. A previously authorized device, even if deemed untrusted by the user, retains the ability to authenticate and establish connections as long as it possesses its original private key and can generate a certificate chaining back to the stored pair data. This undermines the principle of least privilege and complicates incident response efforts where revoking access is required. Furthermore, the encoding inconsistency introduces unpredictability in session management, potentially leading to race conditions or state confusion during authentication attempts that could be leveraged for denial-of-service or further exploitation depending on downstream application logic.
This vulnerability aligns with CWE-295 Improper Certificate Validation and CWE-757 Selection of Less-Secure Algorithm During Negotiation when considering the broader context of cryptographic implementation flaws, though it is most accurately categorized under CWE-345 Insufficient Verification of Data Authenticity due to reliance on chain validation rather than strict identity binding. In terms of offensive security frameworks, this behavior maps directly to MITRE ATT&CK technique T1078 Valid Accounts, specifically the sub-category of Remote Service Authentication Bypass or Account Manipulation, as it allows a previously valid account (the paired client) to regain access despite administrative revocation. It also reflects aspects of T1556 Modification of Client Certificate Trust Store if one considers the storage and retrieval logic flawed in its verification steps.
Mitigation for this vulnerability requires immediate action by updating the Sunshine installation to version 2026.906.222525 or later, where these validation checks have been corrected. Administrators should also audit their list of paired clients to ensure no legacy devices retain active private keys that could be misused if they were running unpatched software in the past. For environments with high security requirements, it is advisable to implement strict certificate pinning policies and regularly rotate client certificates rather than relying on long-term static pairings. Additionally, ensuring that all cryptographic libraries used for PEM parsing enforce canonicalization before comparison will prevent similar encoding-based bypasses in future updates or related software components.