CVE-2009-0547 in Evolution
Summary
by MITRE
Evolution 2.22.3.1 checks S/MIME signatures against a copy of the e-mail text within a signed-data blob, not the copy of the e-mail text displayed to the user, which allows remote attackers to spoof a signature by modifying the latter copy, a different vulnerability than CVE-2008-5077.
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Analysis
by VulDB Data Team • 08/31/2019
The vulnerability described in CVE-2009-0547 represents a critical flaw in the Evolution email client's S/MIME signature verification mechanism. This issue affects Evolution version 2.22.3.1 and demonstrates a fundamental misalignment between the cryptographic verification process and the user interface presentation. The flaw stems from the client's improper handling of signed-data blobs where it validates signatures against an internal copy of email text rather than the text actually rendered for user consumption. This discrepancy creates a security loophole that allows malicious actors to manipulate the email content while maintaining a valid signature, effectively bypassing the integrity protection mechanisms designed to ensure message authenticity.
The technical implementation of this vulnerability involves a mismatch in how Evolution processes S/MIME signed messages. When an email is signed using S/MIME, the signature is generated over specific content within the signed-data structure. However, Evolution's verification process incorrectly references a copy of the email text that exists within the signed-data blob itself, rather than comparing against the actual text displayed to users. This creates a scenario where an attacker can modify the user-facing text while preserving the original signature, as the verification mechanism operates on different data than what is presented. The vulnerability is particularly concerning because it operates at the cryptographic validation layer, where trust assumptions are fundamental to email security protocols.
The operational impact of this vulnerability extends beyond simple message manipulation to encompass potential security breaches and trust violations in email communications. Attackers can exploit this flaw to create convincing phishing attempts or malicious communications that appear legitimate to users due to valid signatures, while simultaneously altering content to include harmful links, commands, or misleading information. This vulnerability essentially undermines the core purpose of digital signatures in email systems, which is to provide assurance that messages have not been tampered with during transit. The implications are particularly severe in enterprise environments where S/MIME signatures are commonly used for secure business communications, as this flaw could enable sophisticated social engineering attacks that bypass traditional signature verification mechanisms.
This vulnerability aligns with CWE-347, which addresses improper certificate validation, and relates to the broader category of cryptographic implementation flaws that compromise security assurances. The issue demonstrates a failure in the principle of least privilege and proper validation, where the system's cryptographic checks are performed against incorrect data sources. From an ATT&CK framework perspective, this vulnerability maps to techniques involving credential access and privilege escalation through manipulation of trusted system components, specifically targeting the email client's signature verification process. The attack vector involves remote execution, where adversaries can craft malicious emails that appear authentic to users while containing modified content, potentially leading to unauthorized access or data compromise. The vulnerability also intersects with defense evasion techniques, as it allows attackers to bypass security controls that rely on signature verification for trust establishment. Organizations should consider implementing additional email security measures such as DKIM validation, spam filtering, and user education to mitigate the risk posed by this flaw, while also ensuring timely updates to email client software to address the underlying cryptographic verification issue.