Executive Summary

CVE-2026-2968 is a vulnerability in Cesanta Mongoose up to version 7.20 that affects the function mg_chacha20_poly1305_decrypt in the file /src/tls_chacha20.c. This function is responsible for handling the Poly1305 Authentication Tag, which is part of the ChaCha20-Poly1305 AEAD cipher used for encryption and authentication.

The vulnerability causes improper verification of the cryptographic signature (Poly1305 authentication tag) during decryption. This means that the authentication guarantees provided by the cipher are bypassed, allowing an attacker to modify encrypted data without detection.

Because ChaCha20 is a stream cipher, this flaw enables a man-in-the-middle attacker to perform precise bit-flipping attacks on any TLS record, modifying encrypted data in transit at the byte level while the server accepts these tampered records as authentic.

The attack can be launched remotely, but it is characterized by high complexity and difficult exploitability. The vendor was contacted but did not respond or provide a fix.

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Impact Analysis

[{'type': 'paragraph', 'content': "This vulnerability impacts the security of TLS connections using Cesanta Mongoose's built-in TLS implementation by allowing attackers to bypass authentication and integrity checks on encrypted data."}, {'type': 'paragraph', 'content': 'An attacker can perform man-in-the-middle bit-flipping attacks on encrypted TLS records, modifying data in transit without detection. This compromises data integrity and could lead to unauthorized data manipulation.'}, {'type': 'paragraph', 'content': 'Since the vulnerability does not require authentication and can be exploited remotely, it poses a risk to any system relying on the affected Mongoose versions for secure communications.'}, {'type': 'paragraph', 'content': 'The lack of vendor response and absence of mitigations means that affected users should consider replacing the vulnerable component to maintain secure communications.'}] [2, 3]

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Compliance Impact

I don't know

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Detection Guidance

There are no specific detection commands or network/system detection methods provided for this vulnerability in the available resources.

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Mitigation Strategies

Immediate mitigation steps are not provided by the vendor, and no known fixes or countermeasures exist.

It is recommended to consider replacing the affected Cesanta Mongoose component with an alternative product to avoid the vulnerability.

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