CVE-2026-81707 in openssl_encrypt
Summary
by MITRE • 08/27/2026
openssl_encrypt before 1.4.9 fails to sanitize the email field of imported identity documents, allowing attackers to inject ANSI escape sequences that forge the fingerprint verification line displayed to users. Attackers can deliver a crafted identity bundle through normal contact-exchange flows or keyserver responses to manipulate terminal output and display a fraudulent fingerprint, bypassing the out-of-band verification mechanism that protects against key substitution attacks.
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Analysis
by VulDB Data Team • 08/27/2026
The vulnerability in OpenSSL versions prior to 1.4.9 represents a critical failure in input sanitization within the identity document import functionality, specifically targeting the email field associated with imported identities. This flaw allows for the injection of ANSI escape sequences into terminal output that is displayed to end-users during cryptographic operations. The core technical issue stems from the application's lack of proper validation or encoding when processing user-supplied data contained in identity bundles. When an attacker crafts a malicious identity bundle containing specially formatted email addresses with embedded control characters, these sequences are passed directly to the standard output stream without being stripped or escaped. This behavior violates fundamental principles of secure coding regarding untrusted input handling and leads to terminal escape sequence injection, which is categorized under CWE-16 as a flaw in configuration settings that allows for unintended information exposure or manipulation.
The operational impact of this vulnerability is severe because it directly undermines the security model designed to prevent key substitution attacks through out-of-band verification. In public key infrastructure systems like GnuPG and OpenSSL-based implementations, users are expected to verify the fingerprint of a received public key against a known-good value obtained via an independent channel such as voice call or in-person meeting. By injecting ANSI escape sequences into the email field that is displayed alongside the identity information, attackers can manipulate the terminal's rendering engine to overwrite or alter the visual presentation of the cryptographic fingerprint line. This manipulation creates a fraudulent display where the user sees a legitimate-looking fingerprint while the actual key being used by the application corresponds to an attacker-controlled key. Consequently, the out-of-band verification mechanism is bypassed because the user trusts the visually presented data which has been artificially constructed through terminal control codes rather than authentic cryptographic derivation.
This attack vector aligns with several entries in the MITRE ATT&CK framework, particularly those related to command and script interpretation or display manipulation techniques used for social engineering. The ability to forge visual output is a sophisticated form of phishing that exploits human trust in graphical user interfaces and terminal outputs. Attackers can deliver these crafted identity bundles through normal contact-exchange flows where users share keys via email or messaging apps, or by uploading them to public key servers which are then retrieved automatically during standard cryptographic operations. The persistence of this vulnerability across multiple versions highlights a systemic oversight in the sanitization logic for non-cryptographic fields that influence user-facing displays.
Mitigation strategies must focus on strict input validation and output encoding. Developers should implement rigorous filtering mechanisms to strip or escape all control characters, including ANSI escape sequences, from any field intended for display purposes before it is passed to the terminal rendering engine. Additionally, adopting a whitelist approach for allowed characters in identity fields can prevent unexpected formatting issues. For users operating with affected versions, manual verification of fingerprints remains essential but must be supplemented by verifying that no anomalous control codes are present in the displayed text if possible through raw output inspection tools until an updated version is deployed. Upgrading to OpenSSL 1.4.9 or later resolves this issue as it includes patches for proper sanitization of identity document fields, ensuring that terminal outputs remain faithful representations of the underlying cryptographic data and preserving the integrity of out-of-band verification processes.