A denial of service vulnerability was identified that exists in Apache SpamAssassin before 3.4.2. The vulnerability arises with certain unclosed tags in emails that cause markup to be handled incorrectly leading to scan timeouts. In Apache SpamAssassin, using HTML::Parser, we setup an object and hook into the begin and end tag event handlers In both cases, the "open" event is immediately followed by a "close" event - even if the tag *does not* close in the HTML being parsed. Because of this, we are missing the "text" event to deal with the object normally. This can cause carefully crafted emails that might take more scan time than expected leading to a Denial of Service. The issue is possibly a bug or design decision in HTML::Parser that specifically impacts the way Apache SpamAssassin uses the module with poorly formed html. The exploit has been seen in the wild but not believed to have been purposefully part of a Denial of Service attempt. We are concerned that there may be attempts to abuse the vulnerability in the future.
This vulnerability carries a MEDIUM severity rating with a CVSS v3.1 score of 5.3, indicating it can be exploited remotely over the network with relatively low complexity without requiring user interaction and does not require pre-existing privileges . The vulnerability impacts and limited availability for affected systems. Impacting 7 products from apache, from canonical, from debian and 4 others, organizations running these solutions should prioritize assessment and patching.
First disclosed in 2018, this vulnerability was reported during a period defined by widespread IoT adoption challenges, mobile security concerns, and the emergence of advanced persistent threat (APT) techniques. Contemporary mitigation strategies focused on secure development practices and third-party component vetting.
2018-09-17T14:29:00.293
2026-06-17T01:08:07.693
Modified
CVSSv3.0: 5.3 (MEDIUM)
AV:N/AC:L/Au:N/C:N/I:N/A:P
10.0
2.9
| Type | Vendor | Product | Version/Range | Vulnerable? |
|---|---|---|---|---|
| Application | apache | spamassassin | < 3.4.2 | Yes |
| Operating System | canonical | ubuntu_linux | 12.04 | Yes |
| Operating System | canonical | ubuntu_linux | 14.04 | Yes |
| Operating System | canonical | ubuntu_linux | 16.04 | Yes |
| Operating System | canonical | ubuntu_linux | 18.04 | Yes |
| Operating System | debian | debian_linux | 8.0 | Yes |
| Operating System | redhat | enterprise_linux_desktop | 7.0 | Yes |
| Operating System | redhat | enterprise_linux_eus | 7.5 | Yes |
| Operating System | redhat | enterprise_linux_server | 7.0 | Yes |
| Operating System | redhat | enterprise_linux_workstation | 7.0 | Yes |
SecUtils normalizes and enriches National Vulnerability Database (NVD) records by standardizing vendor and product identifiers, aggregating vulnerability metadata from both NVD and MITRE sources, and providing structured context for security teams. For apache's affected products, we extract Common Platform Enumeration (CPE) data, Common Weakness Enumeration (CWE) classifications, CVSS severity metrics, and reference data to enable rapid vulnerability prioritization and asset correlation. This record contains no exploit code, proof-of-concept instructions, or attack methodologies—only defensive intelligence necessary for patch management, risk assessment, and security operations.