CVE-2011-3599 in Crypt-DSA
Summary
by MITRE
The Crypt::DSA (aka Crypt-DSA) module 1.17 and earlier for Perl, when /dev/random is absent, uses the Data::Random module, which makes it easier for remote attackers to spoof a signature, or determine the signing key of a signed message, via a brute-force attack.
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Analysis
by VulDB Data Team • 11/23/2021
The vulnerability identified as CVE-2011-3599 affects the Crypt::DSA Perl module version 1.17 and earlier, presenting a significant security weakness in digital signature operations. This flaw manifests when the system lacks access to the /dev/random device, which is a critical source of cryptographically secure random numbers for cryptographic operations. The module's dependency on Data::Random in such environments creates a predictable randomness scenario that undermines the security guarantees of the DSA signature algorithm. The underlying issue stems from the module's inability to properly handle the absence of high-quality random number generation, forcing it to fall back to less secure alternatives that do not provide the necessary entropy for cryptographic security.
The technical flaw resides in the module's random number generation mechanism where the absence of /dev/random triggers a fallback to Data::Random, which does not produce sufficient cryptographic entropy. This weakness directly impacts the DSA signature generation process, as the security of DSA signatures relies heavily on the unpredictability of the random nonce used in each signature operation. When this nonce becomes predictable due to insufficient randomness, attackers can exploit this vulnerability through brute-force attacks to either forge signatures or recover the private signing key. The vulnerability is classified under CWE-330, which addresses the use of insufficiently random values in cryptographic contexts, making it a direct violation of cryptographic best practices and standards.
The operational impact of this vulnerability extends beyond simple signature forgery, as it fundamentally compromises the integrity and authenticity guarantees that DSA signatures are designed to provide. Attackers can leverage this weakness to impersonate legitimate signers, potentially gaining unauthorized access to systems or services that rely on DSA-based authentication. The vulnerability is particularly dangerous in environments where the /dev/random device is not available or accessible, which can occur in containerized environments, virtualized systems, or systems with restricted device access. This makes the attack surface broader than initially apparent, as many modern deployment scenarios may not have the expected random number generation facilities available. The security implications align with ATT&CK technique T1556.004, which involves credential access through the exploitation of cryptographic weaknesses in signature verification systems.
Mitigation strategies for this vulnerability include upgrading to a newer version of the Crypt::DSA module where the random number generation has been properly addressed, ensuring that systems maintain access to appropriate random number generation facilities such as /dev/random or /dev/urandom, and implementing proper fallback mechanisms that maintain cryptographic security even when primary random number sources are unavailable. Organizations should also consider implementing monitoring for systems that may be running vulnerable versions of the module and ensure that all cryptographic operations are performed with sufficient entropy sources. The fix typically involves modifying the random number generation logic to use more robust entropy sources or to properly detect and handle cases where high-quality randomness is not available, thereby preventing the predictable patterns that enable brute-force attacks against the signature scheme.