CVE-2026-40281: Gotenberg has ExifTool stdin argument injection via metadata value newlines (bypass of key sanitization fix)

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 2.1%, percentile 81: FIRST’s model estimates a 2.1% chance of exploitation activity in the next 30 days, higher than 81% of all scored CVEs (elevated). 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 github.com/gotenberg/gotenberg/v8 (Go) <= 8.30.1, fixed in 8.31.0. Check your lockfile, including transitive dependencies.

What it is

Gotenberg is a Docker-powered stateless API for PDF files. In versions 8.30.1 and earlier, the metadata write endpoint validates metadata keys for control characters but leaves metadata values unsanitized. A newline character in a metadata value splits the ExifTool stdin line into two separate arguments, allowing injection of arbitrary ExifTool pseudo-tags such as -FileName, -Directory, -SymLink, and -HardLink. This is a bypass of the incomplete key-sanitization fix introduced in v8.30.1. An unauthenticated attacker can rename or move any PDF being processed to an arbitrary path in the container filesystem, overwrite arbitrary files, or create symlinks and hard links at arbitrary paths.

From the GitHub advisory

Vulnerability Details

CWE: CWE-20 - Improper Input Validation

The metadata value sanitization introduced in v8.30.1 (commit 405f106) only validates metadata KEYS via safeKeyPattern regex. Metadata VALUES are passed unsanitized to go-exiftool SetString(), which writes them as fmt.Fprintln(e.stdin, "-"+k+"="+str). A newline (\n) in a value splits the ExifTool stdin line into two separate arguments, allowing injection of arbitrary ExifTool pseudo-tags such as -FileName, -Directory, -SymLink, -HardLink. Docker-verified: HTTP 404 returned (file moved), /tmp/injectproof created in container. This is a bypass of the incomplete fix in v8.30.1.

Summary

The metadata write endpoint in v8.30.1 validates metadata keys for control characters (commit 405f106) but leaves metadata values unsanitized. go-exiftool's WriteMetadata sends each key/value pair to ExifTool's stdin as:

Weakness type: CWE-88.

Product: github.com/gotenberg/gotenberg/v8 (Go) · Assigned by: GitHub_M · Published: 2026-05-06

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: changed (can affect other components)

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 partial.
• FIRST EPSS (model of 2026-10-21): 2.09% probability of exploitation activity in the next 30 days; percentile 81.

Timeline

• 2026-04-30 — GitHub-reviewed advisory GHSA-q7r4-hc83-hf2q published (critical)
• 2026-05-06 — CVE record published by GitHub_M
• 2026-05-07 — CVE record last updated

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-q7r4-hc83-hf2q github.com
2. CVE.org record CVE-2026-40281 cve.org
3. NVD entry CVE-2026-40281 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

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