AI Threat Alert
CVE-2024-58340
HIGHAny LangChain-based application running MRKL agents on version 0.3.1 or earlier is vulnerable to a DoS attack delivered via prompt injection — no authentication required. An attacker who can influence LLM output (e.g., through user-supplied prompts in a downstream app) can stall your agent service with a single crafted string. Patch to LangChain >0.3.1 immediately; if you cannot patch today, wrap MRKLOutputParser calls with a timeout and sanitize LLM output before parsing.
Affected Systems
| Package | Ecosystem | Vulnerable Range | Patched |
|---|---|---|---|
| langchain | pip | — | No patch |
Do you use langchain? You're affected.
Severity & Risk
Recommended Action
- 1. PATCH: Upgrade langchain to the first version past 0.3.1 that includes the fixed regex; verify with `pip show langchain`. 2. WORKAROUND (if patch is not immediate): Wrap MRKLOutputParser.parse() calls with a signal-based or thread-based timeout (e.g., 2–5 seconds); raise a parsing error and abort on timeout. 3. INPUT HYGIENE: Truncate LLM output to a reasonable maximum length (e.g., 4 KB) before passing to the parser; reject outputs with suspicious repetitive patterns. 4. RATE LIMITING: Apply per-user/session rate limits on agent invocations to reduce DoS throughput. 5. DETECTION: Alert on sustained high CPU usage in agent worker processes; log parsing duration and alert on outliers >500 ms. 6. INVENTORY: Audit all internal and customer-facing apps that import langchain.agents.mrkl.
Classification
Compliance Impact
This CVE is relevant to:
Technical Details
NVD Description
LangChain versions up to and including 0.3.1 contain a regular expression denial-of-service (ReDoS) vulnerability in the MRKLOutputParser.parse() method (libs/langchain/langchain/agents/mrkl/output_parser.py). The parser applies a backtracking-prone regular expression when extracting tool actions from model output. An attacker who can supply or influence the parsed text (for example via prompt injection in downstream applications that pass LLM output directly into MRKLOutputParser.parse()) can trigger excessive CPU consumption by providing a crafted payload, causing significant parsing delays and a denial-of-service condition.
Exploitation Scenario
An attacker targets a public-facing AI assistant built on LangChain MRKL agents. They craft a user prompt designed to cause the underlying LLM to produce output containing a pathological string — for example, a long sequence of spaces or repeated characters that exploits the backtracking in the MRKL action-extraction regex (e.g., `Action: ` followed by thousands of repeated ambiguous characters). The application passes the LLM's raw output directly to MRKLOutputParser.parse() without sanitization. The regex engine enters catastrophic backtracking, pegging one CPU core at 100% for tens of seconds per request. An attacker automating dozens of such requests can exhaust worker threads and render the service unavailable for all users within minutes.
Weaknesses (CWE)
CVSS Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H References
- github.com/langchain-ai/langchain Product
- huntr.com/bounties/e7ece02c-d4bb-4166-8e08-6baf4f8845bb Exploit Issue 3rd Party
- langchain.com Product
- vulncheck.com/advisories/langchain-mrkloutputparser-redos 3rd Party