CVE-2026-40280
Because Go's net/url.Parse() normalizes the scheme to lowercase before establishing the outbound TCP connection, an attacker can bypass the deny-list by simply capitalizing part of the URL scheme (e.g., HTTP://, HTTPS://, or Http://).
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (1.95%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
Description
Gotenberg is an API-based document conversion tool. In versions 8.30.1 and earlier, the default private-IP deny-lists for the --webhook-deny-list and --api-download-from-deny-list flags use a case-sensitive regular expression (^https?://) to match URL schemes. Because Go's net/url.Parse() normalizes the scheme to lowercase before establishing the outbound TCP connection, an attacker can bypass the deny-list by simply capitalizing part of the URL scheme (e.g., HTTP://, HTTPS://, or Http://). This allows unauthenticated requests to reach internal network services, including private IP ranges, loopback addresses, and cloud instance metadata endpoints such as HTTP://169.254.169.254/latest/meta-data/. This bypasses the same security control that was patched in CVE-2026-27018. This issue has been fixed in version 8.31.0.
- CVSS 4.0
- 7.8 HIGHCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M
- EPSS
- 1.95% probability · 79th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-918
- Affected
- thecodingmachine/gotenberg
- Source
- security-advisories@github.com
References
- https://github.com/advisories/GHSA-jjwv-57xh-xr6rNot Applicable
- https://github.com/gotenberg/gotenberg/commit/3f01ca18d3cc21375a1e2da4b5a3f261c8548e47Patch
- https://github.com/gotenberg/gotenberg/security/advisories/GHSA-5q7p-7jgv-ww56Exploit, Mitigation, Vendor Advisory
- https://github.com/gotenberg/gotenberg/security/advisories/GHSA-5q7p-7jgv-ww56Exploit, Mitigation, Vendor Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.