# GHSA-5739-39v2-5754: Impact `RSACrypt::decryptWithRSA15()` (used by the `RSA1_5` key-encryption algorithm) implements RSAES-PKCS1-v1_5 decryption by inspecti

> A timing side-channel in RSA1_5 decryption allows attackers to recover the content encryption key via a padding oracle attack.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 18 Jun 2026

## What is GHSA-5739-39v2-5754?

GHSA-5739-39v2-5754 is a vulnerability in web-token/jwt-library, published on 18 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

### Impact

`RSACrypt::decryptWithRSA15()` (used by the `RSA1_5` key-encryption algorithm) implements RSAES-PKCS1-v1_5 decryption by inspecting the padding after RSADP and throwing `InvalidArgumentException` as soon as the padding is malformed. It does **not** implement the implicit-rejection countermeasure required by RFC 3447 §7.2.2 / RFC 8017 §7.1.2 (return a deterministic pseudo-random value of the expected length on padding failure and let the downstream step fail uniformly).

From a JWE caller this yields a Bleichenbacher/Marvin padding oracle: an attacker submitting adaptively crafted `encrypted_key` values can distinguish (a) padding rejected, (b) padding valid but wrong CEK length, and (c) padding valid and full AEAD executed — even though `JWEDecrypter` returns the same `false` in all cases — because each path performs a measurably different amount of work, amplifiable by enlarging the ciphertext (CWE-208 timing side channel). Enough adaptive queries can recover the wrapped CEK.

### Affected configurations

Applications that register `RSA1_5` in their decryption `AlgorithmManager` and hold an RSA private key.

### Patches

PKCS#1 v1.5 decryption now performs implicit rejection: on invalid padding (or unexpected recovered length) it returns a random CEK of the expected size selected in constant time, so the full content-decryption (AEAD) step always runs and fails uniformly, removing the observable difference between padding-valid and padding-invalid ciphertexts. Users are still strongly encouraged to migrate to `RSA-OAEP`.

### Workarounds

Prefer `RSA-OAEP`/`RSA-OAEP-256`; do not enable `RSA1_5` for untrusted tokens.

### References

- RFC 3447 §7.2.2 / RFC 8017 §7.1.2
- Bleichenbacher (1998); Marvin attack
- CWE-208: Observable Timing Discrepancy

## Résolution

Un correctif a été préparé sur une branche dédiée basée sur `3.4.x`, avec des tests anti-régression dédiés (fork privé temporaire de cette advisory, PR #1).

**RSA1_5** — déchiffrement PKCS#1 v1.5 avec *implicit rejection* en temps constant (RFC 3447 §7.2.2) : un padding invalide n'est plus distinguable d'un padding valide, neutralisant l'oracle Bleichenbacher.

**Validation :** `php -l` OK, PHPUnit vert, aucune nouvelle erreur PHPStan introduite (différentiel nul vs `3.4.x`), aucun commentaire ajouté dans le code source. Après merge, cascade prévue `3.4.x → 4.0.x → 4.1.x`.

## Which versions are affected by GHSA-5739-39v2-5754?

6 open source packages ship an affected version, including web-token/jwt-library.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `web-token/jwt-library` | Packagist | All versions | 3.4.10 |
| `web-token/jwt-library` | Packagist | All versions | 3.4.10 |
| `web-token/jwt-library` | Packagist | From 4.0.0 | 4.0.7 |
| `web-token/jwt-library` | Packagist | From 4.0.0 | 4.0.7 |
| `web-token/jwt-library` | Packagist | From 4.1.0 | 4.1.7 |
| `web-token/jwt-library` | Packagist | From 4.1.0 | 4.1.7 |

## How do I fix GHSA-5739-39v2-5754?

Upgrade web-token/jwt-library to a fixed version for your release line: 3.4.10, 4.0.7 or 4.1.7.

## Is GHSA-5739-39v2-5754 being exploited?

There is no known exploitation of GHSA-5739-39v2-5754 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for GHSA-5739-39v2-5754 and fix it if it is affected.

What it is: GHSA-5739-39v2-5754 is a vulnerability in web-token/jwt-library, published on 18 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of GHSA-5739-39v2-5754 in the wild and no public exploit code.

Affected packages and fixed versions:
- web-token/jwt-library (Packagist): affected all versions; fixed in 3.4.10
- web-token/jwt-library (Packagist): affected all versions; fixed in 3.4.10
- web-token/jwt-library (Packagist): affected from 4.0.0; fixed in 4.0.7
- web-token/jwt-library (Packagist): affected from 4.0.0; fixed in 4.0.7
- web-token/jwt-library (Packagist): affected from 4.1.0; fixed in 4.1.7
- web-token/jwt-library (Packagist): affected from 4.1.0; fixed in 4.1.7

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/GHSA-5739-39v2-5754/ (Markdown: https://insights.sbomify.com/GHSA-5739-39v2-5754/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/GHSA-5739-39v2-5754

---
From sbomify Insights: https://insights.sbomify.com/GHSA-5739-39v2-5754/
Summaries are generated and may contain mistakes; the official description above is the record.