CVE-2026-109426 in Telegram-Stremio
Summary
by MITRE • 10/13/2026
Telegram-Stremio through 5.1.0 contains an insecure storage vulnerability that allows attackers with access to the MongoDB database, backups, or logs to recover the operator's authenticated Telegram session string, which is protected only by a keyless, reversible encoding transform rather than actual encryption. Attackers can round-trip the stored value through the repository's own decode_string function with no secret key to obtain a fully authenticated Telegram session, granting complete control of the operator's Telegram account even when two-step verification is enabled.
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Analysis
by VulDB Data Team • 10/13/2026
The vulnerability identified in Stremio versions up to 5.1.0 represents a critical failure in data protection mechanisms within the application’s integration with the Telegram messaging platform. This flaw falls under the category of insecure storage, specifically categorized as CWE-319: Cleartext Storage of Sensitive Information. The core issue lies in how the application handles sensitive authentication credentials, namely the operator's authenticated Telegram session string. Instead of employing robust cryptographic encryption standards that require a secret key for both encoding and decoding, the developers utilized a reversible encoding transform without any associated secret key. This approach fundamentally misunderstands the distinction between obfuscation and encryption, leaving critical security assets exposed to anyone who gains access to the underlying data storage infrastructure.
The operational impact of this vulnerability is severe because it allows attackers with physical or logical access to the MongoDB database, backup files, or application logs to recover the full authenticated session string. Since the protection mechanism relies solely on a reversible encoding function rather than true encryption, there are no computational barriers preventing an adversary from reversing the transformation. The attacker can simply pass the stored value through the repository's own decode_string function, which requires no secret key, to obtain the plaintext session credentials. This process is straightforward and does not require sophisticated cryptanalysis or brute-force techniques, making it accessible even to attackers with limited technical expertise who have managed to infiltrate the storage layer of the application.
Once the attacker recovers the authenticated Telegram session string, they gain complete control over the operator's Telegram account. This level of access persists regardless of whether two-step verification is enabled on the target account. The reason for this bypass is that the recovered session string acts as a valid authentication token that allows direct login to the service without requiring additional credentials such as passwords or SMS-based codes. Consequently, the presence of multi-factor authentication does not mitigate this specific risk vector because the attacker is not attempting to authenticate via the standard user interface but rather by presenting a pre-authenticated session key directly to the backend services. This effectively nullifies the security benefits provided by two-step verification in this context.
From an industry standards perspective, this vulnerability aligns with ATT&CK technique T1539: Steal Web Session Cookie, although it applies specifically to application-level session tokens rather than browser cookies. It also reflects common pitfalls described in CWE-798: Use of Hard-coded Credentials if the encoding logic itself was embedded insecurely, though the primary classification remains insecure storage due to the lack of encryption for data at rest. The failure to implement proper cryptographic practices violates fundamental principles outlined in OWASP guidelines regarding sensitive data protection and secure key management. Applications handling user sessions must ensure that such tokens are encrypted using strong algorithms with properly managed keys when stored persistently, rather than relying on simple encoding schemes that offer no real security against determined adversaries.
To mitigate this vulnerability, developers should immediately replace the reversible encoding transform with a standard encryption algorithm such as AES-256-GCM or ChaCha20-Poly1305. It is imperative to implement proper key management practices where encryption keys are stored separately from the encrypted data, ideally using hardware security modules or cloud-based key management services rather than hardcoding them within the application source code. Additionally, access controls for the MongoDB database and associated logs must be strictly enforced to limit who can read sensitive fields. Regular security audits should include checks for insecure storage patterns, ensuring that all sensitive user data is protected both in transit and at rest using industry-standard cryptographic protocols.