high CVSS 7.4

CVE-2026-48526·Python vulnerability

PyJWT is a JSON Web Token implementation in Python. Prior to 2.13.0, when the verifier is decoding JSON Web Tokens, while supporting both asymmetric and HMAC algorithms, the library does not validate use of JSON Web Keys in HMAC algorithm, allowing attacker to use the issuer public key as the secret key for HMAC algorithm. This vulnerability is fixed in 2.13.0.

Severity: high
Software: Python
Fixed in: 2.13.0
Published: 2026-05-28

Affected versions

Until: 2.13.0

Fixed in: 2.13.0

How to fix this CVE

Update PyJWT to version 2.13.0 or later to patch an algorithm confusion vulnerability that allows attackers to forge JWT tokens using the issuer's public key as an HMAC secret. This flaw affects applications using PyJWT for token verification without explicit algorithm pinning. Upgrade immediately to prevent unauthorized token generation and potential authentication bypass.

sudo dnf update python3-jwt

Defensia detects this vulnerability

How to check if you are affected

Step 1: Run `python3 -c "import jwt; print(jwt.__version__)"` to check the installed PyJWT version. Versions prior to 2.13.0 are vulnerable.
Step 2: Search your application code for JWT token verification calls using `grep -r "jwt.decode" /path/to/app` and verify that the `algorithms` parameter is explicitly specified (not accepting all algorithms).
Step 3: Review authentication logs for unusual token validation failures or successful validations with unexpected algorithm claims by running `grep -i "jwt\|algorithm" /var/log/auth.log | head -100`.
Step 4: After patching, verify the fix with `python3 -c "import jwt; print(jwt.__version__)"` and confirm version is 2.13.0 or higher, then restart any Python services using PyJWT.

FAQ

What is CVE-2026-48526?

CVE-2026-48526 is an algorithm confusion vulnerability in PyJWT where the library fails to validate that JSON Web Keys are appropriate for the claimed algorithm, allowing an attacker to use the issuer's public key as an HMAC secret to forge valid tokens.

Is CVE-2026-48526 being actively exploited?

No, CVE-2026-48526 is not currently listed as actively exploited by CISA and no public exploit code has been released, though the vulnerability has a high CVSS score of 7.4 and should be prioritized for patching.

What versions of Python are affected by CVE-2026-48526?

All versions of PyJWT prior to 2.13.0 are affected. The vulnerability does not affect Python itself but rather the PyJWT library used for JWT handling in Python applications.

How do I check if my server is vulnerable to CVE-2026-48526?

Run `python3 -c "import jwt; print(jwt.__version__)"` to check your PyJWT version. If it is lower than 2.13.0, your installation is vulnerable and requires immediate update.

Does Defensia detect CVE-2026-48526?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If PyJWT is installed on a monitored server, CVE-2026-48526 will appear in your dashboard with remediation steps.

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References

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