CVE-2025-53890: pyLoad vulnerable to XSS through insecure CAPTCHA

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 1.3%, percentile 70: FIRST’s model estimates a 1.3% chance of exploitation activity in the next 30 days, higher than 70% of all scored CVEs (moderate). 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 pyload-ng (PyPI) < 0.20, fixed in 0.20. Check your lockfile, including transitive dependencies.

What it is

pyload is an open-source Download Manager written in pure Python. An unsafe JavaScript evaluation vulnerability in pyLoad’s CAPTCHA processing code allows unauthenticated remote attackers to execute arbitrary code in the client browser and potentially the backend server. Exploitation requires no user interaction or authentication and can result in session hijacking, credential theft, and full system remote code execution. Commit 909e5c97885237530d1264cfceb5555870eb9546, the patch for the issue, is included in version 0.5.0b3.dev89.

From the GitHub advisory

Summary An unsafe JavaScript evaluation vulnerability in pyLoad’s CAPTCHA processing code allows unauthenticated remote attackers to execute arbitrary code in the client browser and potentially the backend server. Exploitation requires no user interaction or authentication and can result in session hijacking, credential theft, and full system rce.

Details The vulnerable code resides in

The onCaptchaResult() function directly passes CAPTCHA results (sent from the user) into eval() No sanitization or validation is performed on this input A malicious CAPTCHA result can include JavaScript such as fetch() or childprocess.exec() in environments using NodeJS Attackers can fully hijack sessions and pivot to remote code execution on the server if the environment allows it

Reproduction Methods 1. Official Source Installation:

2. Virtual Environment:

Weakness type: CWE-94, CWE-79.

Product: pyload-ng (PyPI) · Assigned by: GitHub_M · Published: 2025-07-14

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 yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 1.30% probability of exploitation activity in the next 30 days; percentile 70.

Timeline

• 2025-07-14 — CVE record published by GitHub_M
• 2025-07-15 — CVE record last updated
• 2025-07-15 — GitHub-reviewed advisory GHSA-8w3f-4r8f-pf53 published (critical)

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-8w3f-4r8f-pf53 github.com
2. CVE.org record CVE-2025-53890 cve.org
3. NVD entry CVE-2025-53890 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