Description
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.
References6
- github.com/python/cpython/commit/1f9958f909c1b41a4ffc0b613ef8ec…
- github.com/python/cpython/commit/4561f6418a691b3e89aef0901f53fe…
- github.com/python/cpython/commit/e31c55121620189a0d1a07b689762d…
- github.com/python/cpython/issues/145264
- github.com/python/cpython/pull/145267
- mail.python.org/archives/list/[email protected]/thre…
Metrics
- CVSS 4.0
-
6.0
MEDIUM
Score source: CNA
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X - EPSS — exploit probability
- 0% percentile: 8 · as of 12 November 2026
- CWE
- CWE-345
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.