Description

An attacker that has valid credentials can submit a Sieve script containing an extreme numeric literal, which causes an out-of-bounds write when the ManageSieve service compiles the script. This causes memory corruption and an observed crash of the ManageSieve process, resulting in denial of service for script management. This might be able to be used for remote code execution. Disable the ManageSieve service if users do not need remote Sieve script management. Update to non-vulnerable version. No publicly available exploits are known.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "4.3",
  "pubDate": "2026-08-28T12:16:28.113Z",
  "pubdate": "2026-08-28T12:16:28.113Z",
  "executiveSummary": "This vulnerability is an out-of-bounds write flaw identified in the ManageSieve service's script compilation logic. The vulnerability is triggered when a user with valid credentials uploads a Sieve script containing an extreme numeric literal, leading to memory corruption.\nThe primary impact of this flaw is a Denial of Service (DoS) resulting from the crash of the ManageSieve process. However, because the vulnerability involves memory corruption, there exists a theoretical risk of remote code execution (RCE).\nExploitation requires the attacker to possess valid credentials for the ManageSieve service. Since it involves script management, the service must be reachable and enabled for an attacker to interact with it. The risk is significant for environments where ManageSieve is exposed, as it allows authenticated users to disrupt service availability or potentially gain unauthorized control over the server environment.",
  "technicalDetails": "The vulnerability resides within the script compilation component of the ManageSieve service, which is responsible for parsing and validating Sieve scripts submitted by users. The root cause is an improper handling of numeric literals within the script structure. Specifically, when the compiler encounters an extreme numeric literal—one that likely exceeds the memory allocation boundaries or the integer type capacity designated for parsing—it performs an out-of-bounds write during the internal compilation or validation phase.\nThe attack flow commences with the attacker establishing an authenticated session with the ManageSieve service. Upon establishing the session, the attacker transmits a specially crafted Sieve script via the appropriate protocol commands. This script includes a malicious numeric literal designed to trigger the out-of-bounds write condition. When the ManageSieve service attempts to compile or process the script, the parser fails to properly validate the memory bounds associated with the literal value. Consequently, the application writes data beyond the allocated buffer memory in the heap or stack.\nThis memory corruption typically results in an immediate crash of the ManageSieve process, leading to a Denial of Service condition for all users relying on the service for script management. From an exploitation perspective, the ability to perform an out-of-bounds write is a critical primitive. If an attacker can precisely control the memory layout, the overwritten data might redirect execution flow, potentially allowing for arbitrary code execution if the attacker can point the instruction pointer to a malicious payload. As the process performs script management, such an exploit would occur within the security context of the user running the ManageSieve daemon, potentially granting the attacker escalated privileges on the host system depending on the service's configuration.\nThe vulnerability is specific to the ManageSieve component and requires valid authentication, acting as a constraint on the attack surface. However, once authentication is obtained, the attacker can leverage the vulnerability without further user interaction. The lack of proper bounds checking on input literals is the primary failure in the component's design, emphasizing the need for robust input sanitization during the compilation phase of the ManageSieve workflow."
}