CVE-2025-48887: 
vLLM vulnerability analysis and mitigation

A Regular Expression Denial of Service (ReDoS) vulnerability was discovered in vLLM (CVE-2025-48887), affecting versions 0.6.4 up to but excluding 0.9.0. The vulnerability exists in the file vllm/entrypoints/openai/tool_parsers/pythonic_tool_parser.py and was disclosed on May 28, 2025. The issue stems from a highly complex and nested regular expression used for tool call detection, which could be exploited by remote attackers to cause severe performance degradation or service unavailability (GitHub Advisory).

The vulnerability is caused by a regular expression pattern containing multiple nested quantifiers (, +), optional groups, and inner repetitions that make it vulnerable to catastrophic backtracking. The problematic regex pattern is: `r"[([a-zA-Z]+\w(([a-zA-Z]+\w=.,\s)([a-zA-Z]+\w=.\s)?),\s)([a-zA-Z]+\w(([a-zA-Z]+\w=.,\s)([a-zA-Z]+\w=.\s)?)\s*)+]"`. The vulnerability has been assigned a CVSS v3.1 score of 6.5 (Medium) with the vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H (GitHub Advisory).

The vulnerability can lead to Denial of Service (DoS) through excessive CPU usage when processing specially crafted payloads. Performance testing showed exponential time complexity growth: a 70-character input took 0.5185 seconds, while a 102-character input required 319.0717 seconds to process. This can result in resource exhaustion, memory retention, and potential GPU memory exhaustion due to unreleased KV cache. The issue may cascade into broader system instability or service downtime (GitHub Advisory).

The vulnerability has been patched in vLLM version 0.9.0. The fix implemented in PR #18454 improved the performance by changing the time complexity from exponential O(2^N) to quadratic O(N^2). While this significantly reduces the vulnerability's impact, it's noted that the regex may still be problematic due to the quadratic complexity (GitHub Advisory).