CVE-2008-1552 in SILC Client
Summary
by MITRE
The silc_pkcs1_decode function in the silccrypt library (silcpkcs1.c) in Secure Internet Live Conferencing (SILC) Toolkit before 1.1.7, SILC Client before 1.1.4, and SILC Server before 1.1.2 allows remote attackers to execute arbitrary code via a crafted PKCS#1 message, which triggers an integer underflow, signedness error, and a buffer overflow. NOTE: the researcher describes this as an integer overflow, but CVE uses the "underflow" term in cases of wraparound from unsigned subtraction.
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Analysis
by VulDB Data Team • 08/07/2019
The vulnerability described in CVE-2008-1552 represents a critical security flaw within the Secure Internet Live Conferencing (SILC) Toolkit ecosystem, specifically affecting versions prior to 1.1.7 for the toolkit, 1.1.4 for the client, and 1.1.2 for the server. This issue resides in the silccrypt library's silc_pkcs1_decode function, which processes PKCS#1 formatted messages during cryptographic operations. The vulnerability manifests when a remote attacker crafts a specially malformed PKCS#1 message that exploits multiple interrelated flaws in the cryptographic processing pipeline, creating a chain of exploitable conditions that ultimately leads to arbitrary code execution on the target system.
The technical exploitation pathway begins with an integer underflow condition that occurs during unsigned arithmetic operations within the PKCS#1 message decoding process. This underflow results from a signedness error where unsigned integer variables are incorrectly handled in subtraction operations, causing the value to wrap around to a large positive number instead of the expected negative result. This wraparound behavior creates a scenario where subsequent buffer allocation calculations produce invalid memory sizes that are significantly smaller than expected. The compromised buffer size then leads directly to a classic buffer overflow condition when the system attempts to write data beyond the allocated memory boundaries, allowing attackers to overwrite adjacent memory regions with malicious content.
The operational impact of this vulnerability extends beyond simple code execution, as it provides attackers with complete control over affected systems running vulnerable versions of the SILC software. The attack vector requires only remote network access to deliver the malicious PKCS#1 message, making it particularly dangerous in networked environments where SILC services are exposed to untrusted clients. This vulnerability directly maps to CWE-190, which describes integer overflow and underflow conditions, and CWE-121, which covers stack-based buffer overflow conditions. The exploitability of this flaw aligns with ATT&CK technique T1059.007, which involves the execution of malicious code through the manipulation of system libraries and cryptographic functions.
Mitigation strategies for CVE-2008-1552 require immediate patching of all affected SILC components to versions 1.1.7 or later, which contain the necessary fixes for the integer underflow and buffer overflow conditions. Organizations should also implement network segmentation to limit access to SILC services and monitor for unusual PKCS#1 message patterns that might indicate exploitation attempts. The fix implemented in the patched versions addresses the root cause by properly validating integer operations and implementing robust bounds checking for buffer allocations, preventing the wraparound conditions that enabled the subsequent buffer overflow. Security teams should conduct comprehensive vulnerability assessments to identify all systems running vulnerable versions of the SILC Toolkit and ensure proper patch management procedures are in place to prevent similar issues in the future.