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CVE-2025-34291

From Exploited flaws, HARD’s guide to the flaws being used in attacks · Checked
This article is about a flaw in Langflow. For every flaw being used in attacks, see Exploited flaws; for Langflow’s, see Langflow flaws being used in attacks.

CVE-2025-34291 is a security flaw in Langflow, a tool for building AI apps. A booby-trapped web page can run an attacker's code through Langflow. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 21 May 2026.[1]

Langflow is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff.

Description

CISA calls it an origin validation error in Langflow Langflow. In its words: “Langflow contains an origin validation error vulnerability in which an overly permissive CORS configuration combined with a refresh token cookie configured as SameSite=None allows a malicious webpage to perform cross-origin requests that include credentials and successfully call the refresh endpoint. This could allow the attacker to execute arbitrary code and achieve full system compromise via obtained tokens that permit access to authenticated endpoints.”[1]

The CVE record adds: “Langflow versions up to and including 1.6.9 contain a chained vulnerability that enables account takeover and remote code execution. An overly permissive CORS configuration (allow_origins='*' with allow_credentials=True) combined with a refresh token cookie configured as SameSite=None allows a malicious webpage to perform cross-origin requests that include credentials and successfully call the refresh endpoint. An attacker-controlled origin can therefore obtain fresh access_token / refresh_token pairs for a victim session. Obtained tokens permit access to authenticated endpoints — including built-in code-execution functionality — allowing the attacker to execute arbitrary code and achieve full system compromise.”[2]

The underlying weakness is CWE-346, in MITRE’s list of common software weaknesses.

It scores 8.8 out of 10 on the Common Vulnerability Scoring System, which rates it high, scored by NVD using CVSS 3.1.[2]

Affected versions

NVD’s record doesn’t list version ranges for it. CISA names the product as Langflow Langflow.

Most families won’t have Langflow; it’s for whoever looks after IT at work.

Exploitation

CISA added it to its catalog of known exploited vulnerabilities on 21 May 2026, 167 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 4 Jun 2026 to fix it.[1]

FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 93%. That’s in the top 1% of the flaws it scores.[3]

CISA assesses it as not automatable: each attack takes some work.

CISA doesn’t say who was attacked, or how.

Fix

CISA’s required action: “Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.”[1]

  1. Check whether you use it.Langflow is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
  2. Send this page to your IT person.Ask them to confirm it’s fixed, or not in use. CISA gave US government agencies until 4 Jun 2026 to fix it.
  3. If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.

You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.

Timeline

DateEvent
The flaw is made public in the National Vulnerability Database, with a severity score of 8.8.[2]
CISA adds it to its catalog of flaws known to be used in attacks.[1]
CISA’s deadline for US government agencies to fix it.[1]
FIRST puts the odds of it being used in attacks in the next 30 days at 93%.[3]

See also

Other Langflow flaws

Added the same day

  • CVE-2026-34926, Trend Micro Apex One: (on-premise) directory traversal ·

Every Langflow flaw on CISA’s list · Everything added in May 2026

References

  1. ^ Cybersecurity and Infrastructure Security Agency. “Langflow Origin Validation Error Vulnerability”. Known Exploited Vulnerabilities Catalog, added 21 May 2026.
  2. ^ National Institute of Standards and Technology. “CVE-2025-34291 Detail”. National Vulnerability Database, published 5 Dec 2025.
  3. ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.928, percentile 99.8, 31 Oct 2026.
  4. CVE Program. “CVE-2025-34291”. The official CVE record.

This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.