CVE-2026-40087: LangChain is a framework for building agents and LLM-powered applications

Q: How do I fix CVE-2026-40087?

langchain core: upgrade to 0.3.84, 1.2.28. Exact commands for each OS are on this page.

Q: Is CVE-2026-40087 being exploited?

CVE-2026-40087 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-40087 affect?

CVE-2026-40087 affects langchain core. Severity is medium (CVSS 5.3). LangChain is a framework for building agents and LLM-powered applications. Prior to 0.3.84 and 1.2.28, LangChain's f-string prompt-template validation was incomplete in two respects. First, some prompt template classes accepted f-string tem

Q: How urgent is CVE-2026-40087?

Priority 28/100. Remotely exploitable, no login, no user action

Routine

MEDIUM 5.3REMOTEUPGRADE

CVE-2026-40087 is a medium-severity flaw (CVSS 5.3) affecting langchain core. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

LangChain is a framework for building agents and LLM-powered applications. Prior to 0.3.84 and 1.2.28, LangChain's f-string prompt-template validation was incomplete in two respects. First, some prompt template classes accepted f-string templates and formatted them without enforcing the same attribute-access validation as PromptTemplate. In particular, DictPromptTemplate and ImagePromptTemplate could accept templates containing attribute access o

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 82%)
CISA exploited list	No
Weakness	CWE-1336
Published	2026-04-09
Last modified	2026-10-25

Publisher (CNA): GitHub, Inc. · Vendor: langchain

Last updated 2026-10-25 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-09 20:16 UTCPublished CVE record published
2026-10-25 23:10 UTCUpdated Record last modified

langchain langchain core UPGRADE

Affected: < 0.3.84 · >= 1.0.0 and < 1.2.28

Fixed in: 0.3.84, 1.2.28

Safe to downgrade to: a release before 1.0.0

1. Check installed version

pip show langchain-core

2. UPGRADE to 0.3.84

pip install --upgrade "langchain-core>=0.3.84"

3. If no update is available yet, DOWNGRADE to a release before 1.0.0

pip index versions langchain-core pip install "langchain-core<1.0.0"

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-40087?

langchain core: upgrade to 0.3.84, 1.2.28. Exact commands for each OS are on this page.

Is CVE-2026-40087 being exploited?

CVE-2026-40087 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-40087 affect?

CVE-2026-40087 affects langchain core. Severity is medium (CVSS 5.3). LangChain is a framework for building agents and LLM-powered applications. Prior to 0.3.84 and 1.2.28, LangChain's f-string prompt-template validation was incomplete in two respects. First, some prompt template classes accepted f-string tem

How urgent is CVE-2026-40087?

Priority 28/100. Remotely exploitable, no login, no user action

Software pages

OpenAI and LLM tools vulnerabilities

References

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