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High

PyJWT vulnerable to key confusion attacks

  • Disclosed: 24.08.2017
  • Updated: 11.10.2026 12:18

In PyJWT 1.5.0 and below the invalid_strings check in HMACAlgorithm.prepare_key does not account for all PEM encoded public keys. Specifically, the PKCS1 PEM encoded format would be allowed because it is prefaced with the string -----BEGIN RSA PUBLIC KEY----- which is not accounted for. This enables symmetric/asymmetric key confusion attacks against users using the PKCS1 PEM encoded public keys, which would allow an attacker to craft JWTs from scratch.

Affected software

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PlatformPackageVulnerable versionsFixed in
Python (PyPI) pyjwt < 1.5.1 1.5.1

References

CVSS score 7.5/10
CVSS vector
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Weakness (CWE)
-
Platform
Python (PyPI)
Package
pyjwt
Disclosed
24.08.2017
Updated
11.10.2026 12:18

Sources and licenses

OSV / GitHub Advisory Database - PYSEC-2017-24 - PyPA Advisory Database; CC BY 4.0

OSV / GitHub Advisory Database - GHSA-r9jw-mwhq-wp62 - CC BY 4.0

Vulnerability history: pyjwt

All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.

All (24) in the archive
Total entries
24
First → latest
08.2017 09.2026
Without a fix
2
Exploited in attacks
0

Severity breakdown

  • Critical 1
  • High 10
  • Medium 11
  • Low 2

Disclosures per year

Severity:
  1. PyJWT: PyJWK accepts empty HMAC keys, bypassing PyJWT's empty-key validation
    High · 7.4 CVE-2026-102266 >= 2.13.0, < 2.14.0 2.14.0
  2. PyJWT: Asymmetric-PEM detection bypass: whitespace/line-ending-mutated public keys skip the HS/asymmetric confusion guard
    Critical · 9.1 CVE-2026-102268 < 2.14.0 2.14.0
  3. PyJWT accepts public JWK containers as HMAC secrets
    High · 7.4 CVE-2026-102273 >= 2.13.0, < 2.14.0 2.14.0
  4. PyJWT: PyJWKClient follows redirects when fetching JWKS
    High · 7.4 CVE-2026-102267 < 2.14.0 2.14.0
  5. PyJWT: Public keys in DER form are accepted as HMAC secrets, bypassing the CVE-2022-29217 guard
    High · 7.4 CVE-2026-102271 >= 2.4.0, < 2.14.0 2.14.0
  6. PyJWT BOM Bypass
    High · 7.4 CVE-2026-102272 >= 2.13.0, < 2.14.0 2.14.0
  7. PyJWT: Public-key JWK accepted as HMAC secret enables forged HS256 tokens when mixed families are allowed
    High · 7.4 CVE-2026-48526 < 2.13.0 2.13.0
  8. PyJWT accepts unknown `crit` header extensions
    High · 7.5 CVE-2026-32597 < 2.12.0 2.12.0
  9. pyjwt v2.10.1 was discovered to contain weak encryption. NOTE: this is disputed by the Supplier because the key length is chosen by the application that uses the library (admittedly, library users may
    High · 7.0 CVE-2025-45768 <= 2.10.1 no fix
  10. Key confusion through non-blocklisted public key formats
    High · 7.4 CVE-2022-29217 >= 1.5.0, < 2.4.0 2.4.0
  11. PyJWT vulnerable to key confusion attacks this entry
    High · 7.5 CVE-2017-11424 < 1.5.1 1.5.1

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