CVE-2010-0562 in fetchmail
Summary
by MITRE
The sdump function in sdump.c in fetchmail 6.3.11, 6.3.12, and 6.3.13, when running in verbose mode on platforms for which char is signed, allows remote attackers to cause a denial of service (application crash) or possibly execute arbitrary code via an SSL X.509 certificate containing non-printable characters with the high bit set, which triggers a heap-based buffer overflow during escaping.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 04/30/2026
The vulnerability described in CVE-2010-0562 represents a critical heap-based buffer overflow in the fetchmail email retrieval utility, specifically affecting versions 6.3.11 through 6.3.13. This flaw exists within the sdump function located in sdump.c, which is responsible for processing and displaying SSL X.509 certificate information during verbose operations. The vulnerability manifests when fetchmail operates in verbose mode on systems where the char data type is signed, creating a condition where maliciously crafted X.509 certificates can trigger memory corruption. The attack vector involves sending an SSL certificate containing non-printable characters with the high bit set, which the sdump function fails to properly handle during its escaping process. This particular vulnerability falls under the CWE-121 heap-based buffer overflow classification, which is categorized under the broader CWE-787 out-of-bounds write weakness. The flaw demonstrates characteristics consistent with the ATT&CK technique T1203, where adversaries exploit software vulnerabilities to cause application crashes or potentially achieve arbitrary code execution, making it a significant concern for systems relying on fetchmail for email retrieval.
The technical implementation of this vulnerability exploits the fundamental mismatch between signed and unsigned character handling in C programming, particularly when processing certificate data. When the sdump function encounters X.509 certificates with high-bit set characters during verbose output operations, the function's escaping mechanism fails to properly account for the signed nature of char on the target platform. This causes the buffer overflow to occur in heap memory allocation, where the function attempts to write beyond the allocated buffer boundaries during the certificate data processing. The vulnerability is particularly insidious because it can be triggered remotely through the SSL certificate validation process without requiring authentication or special privileges from the attacker. The heap corruption can result in immediate application termination, creating a denial of service condition, or potentially allow for arbitrary code execution if the attacker can control the memory layout and overwrite critical program structures. This vulnerability exemplifies the common security pitfalls associated with improper input validation and buffer management in cryptographic software components, where the interaction between different system architectures and software implementations creates exploitable conditions.
The operational impact of CVE-2010-0562 extends beyond simple service disruption to potentially enable remote code execution on affected systems, making it a critical concern for organizations relying on fetchmail for email processing. Systems running fetchmail in verbose mode are particularly vulnerable, as this mode enables the problematic sdump function to process certificate data that would otherwise remain unprocessed. The vulnerability affects not only individual user systems but also enterprise email servers and relay systems that depend on fetchmail for email retrieval operations. Organizations using fetchmail for automated email processing or those operating in environments where SSL certificate validation is critical may experience service interruptions or potential compromise. The exploitability of this vulnerability is enhanced by the fact that it can be triggered through normal email retrieval operations without requiring user interaction, making it particularly dangerous in automated environments. Security professionals should note that this vulnerability represents a classic example of how seemingly benign input processing functions can become attack vectors when dealing with cryptographic certificate data. The impact is further amplified by the fact that many email systems rely on fetchmail or similar utilities for retrieving mail from remote servers, creating a wide attack surface for potential exploitation.
Mitigation strategies for CVE-2010-0562 should prioritize immediate patching of affected fetchmail versions, with particular attention to upgrading to versions 6.3.14 or later where the vulnerability has been addressed. Organizations should disable verbose mode in fetchmail configurations when not actively debugging, as this significantly reduces the attack surface for exploitation. System administrators should implement network-level controls to restrict access to fetchmail services and monitor for unusual certificate validation patterns that might indicate exploitation attempts. The vulnerability can be mitigated through proper input validation and bounds checking in the sdump function, ensuring that certificate data with high-bit characters is properly escaped and handled without exceeding buffer boundaries. Security monitoring should include detection of abnormal application crashes or memory allocation patterns that might indicate heap corruption. Additionally, organizations should consider implementing certificate pinning or other certificate validation controls to reduce the impact of potentially malicious certificate data. The fix for this vulnerability typically involves proper bounds checking in the certificate data processing logic and ensuring that character handling accounts for platform-specific signed/unsigned character behavior. This remediation approach aligns with industry best practices for preventing buffer overflow vulnerabilities and demonstrates the importance of thorough input validation in security-critical cryptographic software components.