High Denial of service exploit reference

CVE-2024-58340 — LangChain <= 0.3.1 MRKLOutputParser ReDoS

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.

Published Jan 12, 2026 · Updated Oct 13, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: VulnCheck

Low

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.

How the score was calculated

EPSS 0.5% (30-day exploitation probability)+6
Technical severity (high)+6
CISA SSVC: exploitation "poc"+5
Automatable exploitation (SSVC)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation

Not confirmed

Not in CISA KEV — an absence of record, not proof it is unexploited.

EPSS FIRST

0.48%

ahead of 40% of scored CVEs · Oct 14, 2026

Affects

Langchain

Langchain and 1 more

CVSS base

7.5

High · 3 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation

Proof of concept

none · proof-of-concept · active

Automatable

Yes

can an attacker script the kill-chain steps

Technical impact

Partial

partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (Langchain Langchain, Langchain-ai Langchain-ai/langchain).
The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
No fix documented in the sources: reduce exposure and monitor the vendor advisory.
Search available logs for exploit probes matching the vulnerability class (denial of service), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
Langchain	Langchain	≤ 0.3.1	Vulnerable	NIST National Vulnerability Database
Langchain-ai	Langchain-ai/langchain	≤ 0.3.1	Vulnerable	CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector

Network

Attack complexity

Low

Privileges required

None

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Scored by
8.7	CVSS 4.0	High	—	—	disclosure@vulncheck.com via NIST National Vulnerability Database
8.7	CVSS 4.0	High	—	—	VulnCheck via CVE Program (cve.org) e CISA ADP
7.5	CVSS 3.1	High	3.9	3.6	nvd@nist.gov via NIST National Vulnerability Database

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H (score shown at the top: nvd@nist.gov)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-1333 · Inefficient Regular Expression Complexity (ReDoS)

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.48%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
Track CPU/memory spikes and availability drops correlated with request patterns.

web/proxy/WAF logsnetwork IDS/IPSresource metrics

Timeline

What happened to this CVE, newest first.

2026
Affected products added · langchain ai/langchain
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
SSVC assessment updated
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
Record published
Oct 13, 2026
CVSS changed · 7.5
Oct 13, 2026 · NIST National Vulnerability Database
Source status changed · → Analyzed
Oct 13, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 13, 2026 · NIST National Vulnerability Database
CVE published
Jan 12, 2026 · VulnCheck

Source activity

Repeated readings are counted rather than listed.

1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

4 on the record

huntr.com/bounties/e7ece02c-d4bb-4166-8e08-6baf4f8845bb
Exploit, Issue Tracking, Third Party Advisory, technical-description, exploit, NIST National Vulnerability Database
www.vulncheck.com/advisories/langchain-mrkloutputparser-redos
Third Party Advisory, third-party-advisory, NIST National Vulnerability Database
www.langchain.com/
Product, product, NIST National Vulnerability Database
github.com/langchain-ai/langchain
Product, product, NIST National Vulnerability Database

Elsewhere on this site

Langchain
every CVE for this vendor

Denial of service
same class

CWE-1333
other pages naming this weakness

Related CVEs (same products)

Medium CVE-2026-55443 LangChain: Path traversal and sandbox escape in LangChain file-search middleware and loaders Jun 22, 2026
High CVE-2026-44843 LangChain: Unsafe deserialization of attacker-controlled LangChain objects through overly broad `load()` allowlists May 26, 2026
Medium CVE-2026-40087 LangChain has incomplete f-string validation in prompt templates Apr 9, 2026
High CVE-2026-34070 LangChain Core has Path Traversal vulnerabilites in legacy `load_prompt` functions Mar 31, 2026
Low CVE-2026-26013 LangChain affected by SSRF via image_url token counting in ChatOpenAI.get_num_tokens_from_messages Feb 10, 2026
High CVE-2025-68664 LangChain serialization injection vulnerability enables secret extraction in dumps/loads APIs Dec 23, 2025

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No fixed version, patch or mitigation documented.
No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2024-58340 is "LangChain <= 0.3.1 MRKLOutputParser ReDoS", rated High. It affects Langchain (Langchain); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 7.5 describes technical severity. EPSS 0.48% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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