| Component | LangChain |
| Severity | high (CVSS 7.5) |
| CVSS vector | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
| Published (NVD) | 2026-01-12 |
| Last modified | 2026-07-14 |
| Affected versions | langchain <= 0.3.1 |
| Fixed in | see the vendor advisory |
| Weakness | CWE-1333 |
| CISA KEV | not listed |
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.
What to do
- NVD lists no fixed version yet: follow the vendor advisory below and keep LangChain off the public internet until a fix ships.
- Do not expose the component's API or UI to the internet without authentication in front of it.
Sources
- NVD: CVE-2024-58340
- https://huntr.com/bounties/e7ece02c-d4bb-4166-8e08-6baf4f8845bb
- https://www.vulncheck.com/advisories/langchain-mrkloutputparser-redos
- https://github.com/langchain-ai/langchain
- https://www.langchain.com/
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