The pure-Erlang RSAES-PKCS1-v15 decryption in the josejwapkcs1 module is a Bleichenbacher padding oracle.
CVE-2026-65626
The pure-Erlang RSAES-PKCS1-v15 decryption in the josejwapkcs1 module is a Bleichenbacher padding oracle. emepkcs1decode/2 returns the recovered message when a decrypted block has valid PKCS#1 v1.5 padding (a leading 0x00 0x02, a padding string of at least eight non-zero bytes, and a 0x00 separator) and returns a distinct error result otherwise, and rsaespkcs1decrypt/2 additionally returns {error, {badsize, }} when the length check fails. The implementation applies no implicit-rejection countermeasure (RFC 8017 §7.2.2): it does not substitute a deterministic pseudo-random plaintext on a padding failure, so a one-bit padding-conformance signal leaks to the caller. Because the underlying modular exponentiation in dp/2 is a raw, non-blinded crypto:modpow/3, the padding check also stays distinguishable by timing even when an application normalizes every failure to a single error value. An unauthenticated attacker who knows only the public RSA key and can submit ciphertexts to a decryption endpoint that unwraps RSA15 JWE keys (or otherwise calls decryptprivate/3 with rsapkcs1padding) can use this oracle to recover the plaintext of intercepted ciphertexts, such as content-encryption…
Assessment
- CVSS
- 5.9 (v4.0)
- Severity
- Medium
- Known exploited
- Not listed in CISA KEV
- Exploit availability
- Nothing found in Exploit-DB, Metasploit, Nuclei or public PoC repositories
- Published
- 26 October 2026
- Last updated
- 27 October 2026
- Weakness
- CWE-203
- Assigner
- 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
CVSS vectorCVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
At the source
References
- https://cna.erlef.org/cves/CVE-2026-65626.html
- https://github.com/potatosalad/erlang-jose/commit/0eac8cef9aaa48fb6846f4e47a0002dc4a73966d
- https://github.com/potatosalad/erlang-jose/commit/853c5d4c4c0bd2a7ecb055b237f4284184e176c8
- https://github.com/potatosalad/erlang-jose/security/advisories/GHSA-vwvr-f994-6j9j
- https://osv.dev/vulnerability/EEF-CVE-2026-65626
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