Vulnerability · Published Apr 10, 2026 · Assigned by PSF
CVE-2026-3446Base64 decoding stops at first padded quad by default
Medium 6.0
In plain English
A medium-severity insufficient verification of data authenticity in CPython from Python Software Foundation. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 9% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | python3.11 | no fix listed | DEBIAN-CVE-2026-3446 |
| Debian:13 | python3.13 | 3.13.5-2+deb13u2 | DEBIAN-CVE-2026-3446 |
| Debian:14 | python3.14 | 3.14.4-1 | DEBIAN-CVE-2026-3446 |
| Ubuntu:22.04:LTS | pypy3 | no fix listed | UBUNTU-CVE-2026-3446 |
| Ubuntu:24.04:LTS | pypy3 | no fix listed | UBUNTU-CVE-2026-3446 |
| Ubuntu:25.10 | pypy3 | no fix listed | UBUNTU-CVE-2026-3446 |
| Ubuntu:26.04:LTS | pypy3 | no fix listed | UBUNTU-CVE-2026-3446 |
| Ubuntu:26.10 | pypy3 | no fix listed | UBUNTU-CVE-2026-3446 |
| Ubuntu:22.04:LTS | python3.10 | no fix listed | UBUNTU-CVE-2026-3446 |
| Ubuntu:24.04:LTS | python3.12 | no fix listed | UBUNTU-CVE-2026-3446 |
| Ubuntu:25.10 | python3.13 | no fix listed | UBUNTU-CVE-2026-3446 |
| Ubuntu:25.10 | python3.14 | no fix listed | UBUNTU-CVE-2026-3446 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Python Software Foundation | CPython | 0 – before 3.13.133.14.0 – before 3.14.43.15.0a1 – before 3.15.0a8 |
Weakness: CWE-345 · 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
References
- https://github.com/python/cpython/pull/145267 patch
- https://github.com/python/cpython/issues/145264 issue-tracking
- https://mail.python.org/archives/list/security-announce@python.org/thread/F5ZT5ICGJ6CKXVUJ34YBVY7WOZ5SHG53/ vendor-advisory
- https://github.com/python/cpython/commit/1f9958f909c1b41a4ffc0b613ef8ec8fa5e7c474 patch
- https://github.com/python/cpython/commit/4561f6418a691b3e89aef0901f53fe0dfb7f7c0e patch
- https://github.com/python/cpython/commit/e31c55121620189a0d1a07b689762d8ca9c1b7fa patch