CVE-2021-29443
MEDIUMCVE-2021-29443 is a medium-severity (CVSS 5.9) CWE-203 vulnerability in jose. O3 Security confirms whether CVE-2021-29443 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Padding Oracle Attack due to Observable Timing Discrepancy in jose
Blast Radius
Weekly download volume for affected packages — a proxy for how broadly this vulnerability is deployed.
josenpmDescription
jose is an npm library providing a number of cryptographic operations. In vulnerable versions AES_CBC_HMAC_SHA2 Algorithm (A128CBC-HS256, A192CBC-HS384, A256CBC-HS512) decryption would always execute both HMAC tag verification and CBC decryption, if either failed JWEDecryptionFailed would be thrown. A possibly observable difference in timing when padding error would occur while decrypting the ciphertext makes a padding oracle and an adversary might be able to make use of that oracle to decrypt data without knowing the decryption key by issuing on average 128*b calls to the padding oracle (where b is the number of bytes in the ciphertext block). All major release versions have had a patch released which ensures the HMAC tag is verified before performing CBC decryption. The fixed versions are ^1.28.1 || ^2.0.5 || >=3.11.4. Users should upgrade their v1.x dependency to ^1.28.1, their v2.x dependency to ^2.0.5, and their v3.x dependency to ^3.11.4. Thanks to Jason from Microsoft Vulnerability Research (MSVR) for bringing this up and Eva Sarafianou (@esarafianou) for helping to score this advisory.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | jose | ≥ 1.0.0&&< 1.28.1 | 1.28.1 |
| 📦npm | jose | ≥ 2.0.0&&< 2.0.5 | 2.0.5 |
| 📦npm | jose | ≥ 3.0.0&&< 3.11.4 | 3.11.4 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for jose. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update jose to 1.28.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-29443 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2021-29443 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2021-29443. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2021-29443 in your dependencies?
O3 detects CVE-2021-29443 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.