CVE-2026-3446 PUBLISHED

Base64 decoding stops at first padded quad by default

Assigner: PSF
Reserved: 02.03.2026 Published: 10.04.2026 Updated: 10.04.2026

When calling base64.b64decode() or related functions the decoding process would stop after encountering the first padded quad regardless of whether there was more information to be processed. This can lead to data being accepted which may be processed differently by other implementations. Use "validate=True" to enable stricter processing of base64 data.

Metrics

CVSS Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
CVSS Score: 6

Product Status

Vendor Python Software Foundation
Product CPython
Versions Default: unaffected
  • affected from 0 to 3.13.13 (excl.)
  • affected from 3.14.0 to 3.14.4 (excl.)
  • affected from 3.15.0a1 to 3.15.0a8 (excl.)

Credits

  • Serhiy Storchaka reporter

References