Improper Message Integrity Enforcement in Erlang/OTP SSL

Impact Analysis

This vulnerability allows a network-positioned attacker to inject unauthenticated plaintext data into a TLS client during the handshake process.

The injected data is delivered to the client application after the handshake completes, potentially misleading the client into treating unauthenticated data as if it were authenticated server data.

However, the attacker cannot observe the client's response or steer the connection, limiting the impact to blind injection without control over the connection.

The injection window is wider for TLS versions prior to TLS 1.3, meaning older TLS versions are more vulnerable to this attack.

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Executive Summary

CVE-2026-54891 is a vulnerability in the Erlang/OTP ssl module, specifically in the tls_gen_connection module, where a network-positioned attacker can inject unauthenticated plaintext APPLICATION_DATA during the TLS handshake.

The issue arises because the function tls_gen_connection:handle_protocol_record/3 rejects APPLICATION_DATA records in pre-handshake states only when the TLS endpoint acts as a server, but does not apply this check when acting as a client.

As a result, an attacker can send plaintext APPLICATION_DATA records to the client during the handshake. These records are buffered and, once the handshake completes successfully, delivered to the application as if they were authenticated post-handshake data.

The attacker cannot observe the client's response or control the connection, so the impact is limited to blind injection of unauthenticated bytes. The vulnerability affects TLS versions prior to TLS 1.3 more severely than TLS 1.3.

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Detection Guidance

This vulnerability involves the injection of unauthenticated plaintext APPLICATION_DATA records during the TLS handshake, which are then accepted by the TLS client after handshake completion. Detection would involve monitoring TLS handshake traffic for unexpected plaintext application data packets sent to the client before handshake completion.

Since the attacker injects plaintext APPLICATION_DATA during the handshake, network monitoring tools could be used to detect such anomalies by inspecting TLS handshake packets for unexpected application data records.

However, no specific detection commands or tools are provided in the available resources.

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Mitigation Strategies

The primary mitigation is to upgrade the Erlang/OTP and ssl versions to the fixed releases where this vulnerability has been addressed.

• Upgrade OTP to version 29.0.3, 28.5.0.3, or 27.3.4.14 or later.
• Upgrade the ssl application to versions 11.7.3, 11.6.0.3, or 11.2.12.10 or later.

These updates include hardening in the tls_gen_connection module that reject unexpected application data before handshake completion, terminating the connection with a fatal alert if such data is detected.

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Compliance Impact

This vulnerability allows a network-positioned attacker to inject unauthenticated plaintext data into a TLS client during the handshake, which the client later treats as authenticated server data. Although the attacker cannot observe or control the client's response, the injection of unauthenticated data could potentially undermine the integrity and confidentiality guarantees expected from TLS communications.

Such a weakness in the TLS communication channel could impact compliance with standards and regulations like GDPR and HIPAA, which require protection of data integrity and confidentiality during transmission. The improper enforcement of message integrity may lead to risks of data tampering or injection attacks, which could be considered a failure to adequately protect sensitive data in transit.

However, the specific impact on compliance depends on the context of use, the sensitivity of the data transmitted, and whether the affected systems have implemented the patched versions that fix this vulnerability.

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