CVE-2026-55536: PraisonAI has a Browser Server WebSocket origin validation bypass via unanchored regex (patch bypass of CVE-2026-40289 / GHSA-8x8f-54wf-vv92)

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.5%, percentile 43: FIRST’s model estimates a 0.5% chance of exploitation activity in the next 30 days, higher than 43% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes PraisonAI (PyPI) < 4.6.58, fixed in 4.6.58. Check your lockfile, including transitive dependencies.

What it is

PraisonAI is a multi-agent teams system. Prior to praisonai 4.6.58, Browser Server handleconnection() checks Chrome extension origins with re.match() and the unanchored expression chrome-extension://[a-z0-9]{32}. Extra trailing characters pass before websocket.accept(), allowing startsession commands and unauthorized browser automation. This issue is fixed in version 4.6.58.

From the GitHub advisory

Summary

praisonai/browser/server.py validates incoming WebSocket connections using a Chrome extension Origin check. The regex chrome-extension://[a-z0-9]{32} is applied with re.match(), which only anchors at the start of the string, not the end. Any Origin header with more than 32 alphanumeric characters after chrome-extension:// — including non-alphanumeric trailing characters — passes the check.

This is a patch bypass of GHSA-8x8f-54wf-vv92. That advisory triggered the addition of origin validation; this finding shows the validation is bypassable by any WebSocket client that forges an Origin header. After bypassing, the attacker can send startsession commands that are executed by any Chrome extension currently connected to the server — causing the extension to perform arbitrary browser automation including cookie theft and screenshot capture.

Details

Vulnerable code — browser/server.py line 186:

Weakness type: CWE-284, CWE-625.

Product: PraisonAI (PyPI) · Assigned by: GitHub_M · Published: 2026-08-25

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable no, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.52% probability of exploitation activity in the next 30 days; percentile 43.

Timeline

• 2026-08-25 — CVE record published by GitHub_M
• 2026-08-25 — GitHub-reviewed advisory GHSA-6g6r-q6gw-w8fg published (critical)
• 2026-08-28 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-6g6r-q6gw-w8fg github.com
2. CVE.org record CVE-2026-55536 cve.org
3. NVD entry CVE-2026-55536 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com

Critical PyPI advisories · Today’s Security Digest