Base64 decoding stops at first padded quad by default
Python Software Foundation · CPython
6.0MediumCVSS 4.0
Recommended action
Scheduled
Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority.
Patch available
Distribution package intelligence
Ubuntu vendor package status
Canonical’s release and source-package findings are shown separately from local repository availability.
2 package states
Repository candidate not checked
A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.
Ubuntu release
Source package
Vendor state
Fixed version
Evidence
Ubuntu 24.04 LTSnoble · standard archive
pypy3
Under evaluationCanonical reports that the package might be affected and still needs evaluation or fixing.
Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.
1 current
CVE-2026-3446 · CSAF 2.0 · revision 3 · finalRed Hat Product Securitypython: Python base64: Incomplete data decoding due to premature stop at padding
30 known affected
The vendor explicitly identifies these products as affected by this CVE.
python3.14 as a component of Red Hat Enterprise Linux 10
python3.14-debug as a component of Red Hat Enterprise Linux 10
python3.14-devel as a component of Red Hat Enterprise Linux 10
python3.14-freethreading as a component of Red Hat Enterprise Linux 10
python3.14-freethreading-debug as a component of Red Hat Enterprise Linux 10
python3.14-freethreading-devel as a component of Red Hat Enterprise Linux 10
python3.14-freethreading-idle as a component of Red Hat Enterprise Linux 10
python3.14-freethreading-libs as a component of Red Hat Enterprise Linux 10
python3.14-freethreading-test as a component of Red Hat Enterprise Linux 10
python3.14-freethreading-tkinter as a component of Red Hat Enterprise Linux 10
python3.14-idle as a component of Red Hat Enterprise Linux 10
python3.14-libs as a component of Red Hat Enterprise Linux 10
Summary
A flaw was found in the Python base64 module. When decoding base64 data using functions like base64.b64decode(), the decoding process prematurely stops upon encountering the first padding character. This can result in incomplete data being processed, where any information following the initial padding is unexpectedly ignored. Consequently, applications might interpret or handle base64-encoded data inconsistently compared to other implementations, potentially leading to data integrity issues.
Remediation
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://images.redhat.com/
Optional official sources
National CERT insights ?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.
Select the national-authority views to include. The exact source language is shown on each matched advisory. Your choice is remembered on this device and encoded in the shareable URL.
Official European source
ENISA European Vulnerability Database
Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.
1 current
ENISA EUVD identifier
EUVD-2026-21545
No EUVD known-exploited evidence
ENISA has published the identifier mapping but no EUVD description has been stored yet.
EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
Not supplied in the stored EUVD record
Advisory evidence
No linked advisory details stored yet
Recommended actionScheduled
Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority.
Patch available
01
What, why and how
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.
What
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.
Why
The product does not sufficiently verify the origin or authenticity of data, in a way that causes it to accept invalid data.
How
An attacker operating through a network path may attempt exploitation with low privileges. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.
What
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.
Why
The product does not sufficiently verify the origin or authenticity of data, in a way that causes it to accept invalid data.
How
An attacker operating through a network path may attempt exploitation with low privileges. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.
02
Exploit reality and attack path
CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.
Observed exploitation ?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.No confirmed evidence
No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.
Public PoC / exploit material ?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.None recorded
No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.
Likely attack path
a network path → Insufficient Verification of Data Authenticity → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface
Network
Privileges required
Low: a basic authenticated account is required
User interaction
None
Attack complexity
High: exploitation depends on specific conditions
Security boundary
Not a CVSS 4.0 base metric
Weakness ?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-345: Insufficient Verification of Data Authenticity. The product does not sufficiently verify the origin or authenticity of data, in a way that causes it to accept invalid data.
CVSS vector ?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
Common Vulnerability Scoring System 4.0: the compact vector below is decoded into plain language.
AVNetworkAttack vector: The vulnerable component can be reached over a network.ACHighAttack complexity: Successful exploitation depends on specific conditions outside the attacker's direct control.ATPresentAttack requirements: A particular deployment or execution condition must be present.PRLowPrivileges required: The attacker needs basic user-level privileges.UINoneUser interaction: No action by another user is required.VCNoneVulnerable-system confidentiality: No direct loss is represented by this metric.VIHighVulnerable-system integrity: A successful attack can cause a major loss.VANoneVulnerable-system availability: No direct loss is represented by this metric.SCNoneSubsequent-system confidentiality: No direct loss is represented by this metric.SINoneSubsequent-system integrity: No direct loss is represented by this metric.SANoneSubsequent-system availability: No direct loss is represented by this metric.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkCWE-345
A
Official authority intelligence
Only matched European and national findings are included. Language selectors and unavailable sources are omitted.
ENISA EUVD · EUVD-2026-21545Official EUVD mapping
0 linked advisory records.
Official EUVD recordBSI · German · WID-SEC-W-2026-1064CPython: Mehrere Schwachstellen
Ein Angreifer kann mehrere Schwachstellen in CPython ausnutzen, um Sicherheitsvorkehrungen zu umgehen, und um Daten zu manipulieren.
Official advisoryCERT-FR · French · CERTFR-2026-AVI-0556Multiples vulnérabilités dans les produits VMware
Official advisoryCERT-FR · French · CERTFR-2026-AVI-0426Multiples vulnérabilités dans Python
De multiples vulnérabilités ont été découvertes dans Python. Elles permettent à un attaquant de provoquer un contournement de la politique de sécurité et un problème de sécurité non spécifié par l'éditeur.
Operational remediation based on structured source evidence.
Status ?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Patch available
Affected
python3.14 as a component of Red Hat Enterprise Linux 10; python3.14-debug as a component of Red Hat Enterprise Linux 10; python3.14-devel as a component of Red Hat Enterprise Linux 10; python3.14-freethreading as a component of Red Hat Enterprise Linux 10; python3.14-freethreading-debug as a component of Red Hat Enterprise Linux 10; python3.14-freethreading-devel as a component of Red Hat Enterprise Linux 10; python3.14-freethreading-idle as a component of Red Hat Enterprise Linux 10; python3.14-freethreading-libs as a component of Red Hat Enterprise Linux 10; python3.14-freethreading-test as a component of Red Hat Enterprise Linux 10; python3.14-freethreading-tkinter as a component of Red Hat Enterprise Linux 10; python3.14-idle as a component of Red Hat Enterprise Linux 10; python3.14-libs as a component of Red Hat Enterprise Linux 10; python3.14-test as a component of Red Hat Enterprise Linux 10; python3.14-tkinter as a component of Red Hat Enterprise Linux 10; python3.14.src as a component of Red Hat Enterprise Linux 10; python3.14 as a component of Red Hat Enterprise Linux 9; python3.14-debug as a component of Red Hat Enterprise Linux 9; python3.14-devel as a component of Red Hat Enterprise Linux 9; python3.14-freethreading as a component of Red Hat Enterprise Linux 9; python3.14-freethreading-debug as a component of Red Hat Enterprise Linux 9; python3.14-freethreading-devel as a component of Red Hat Enterprise Linux 9; python3.14-freethreading-idle as a component of Red Hat Enterprise Linux 9; python3.14-freethreading-libs as a component of Red Hat Enterprise Linux 9; python3.14-freethreading-test as a component of Red Hat Enterprise Linux 9; python3.14-freethreading-tkinter as a component of Red Hat Enterprise Linux 9; python3.14-idle as a component of Red Hat Enterprise Linux 9; python3.14-libs as a component of Red Hat Enterprise Linux 9; python3.14-test as a component of Red Hat Enterprise Linux 9; python3.14-tkinter as a component of Red Hat Enterprise Linux 9; python3.14.src as a component of Red Hat Enterprise Linux 9
Fixed
python3-11-main@aarch64 as a component of Red Hat Hardened Images; python3-11-main@src as a component of Red Hat Hardened Images; python3-11-main@x86_64 as a component of Red Hat Hardened Images; python3-12-main@aarch64 as a component of Red Hat Hardened Images; python3-12-main@src as a component of Red Hat Hardened Images; python3-12-main@x86_64 as a component of Red Hat Hardened Images; python3-13-main@aarch64 as a component of Red Hat Hardened Images; python3-13-main@src as a component of Red Hat Hardened Images; python3-13-main@x86_64 as a component of Red Hat Hardened Images; python3-14-main@aarch64 as a component of Red Hat Hardened Images; python3-14-main@noarch as a component of Red Hat Hardened Images; python3-14-main@src as a component of Red Hat Hardened Images; python3-14-main@x86_64 as a component of Red Hat Hardened Images
Action
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://images.redhat.com/
Workaround
No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04
Evidence and provenance
Published 10 Apr 2026 · Last source change 13 Apr 2026, 16:07 UTC · CWE-345 · Insufficient Verification of Data Authenticity
CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source ?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2026-21545
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCISA ADP
NVD statusNVD awaiting enrichment
Core structured fields are present and their contributing authorities are shown above.
Affected versionsThe structured affected or fixed version information changed.
Before
python3.14 as a component of Red Hat Enterprise Linux 10; python3.14-debug as a component of Red Hat Enterprise Linux 10; python3.14-devel as a component of Red Hat Enterprise Linux 10; python3.14-freethreading as a component of Red Hat Enterprise Linux 10; python3.14-freethreading-debug as a component of Red Hat Enterprise Linux 10; python3.14-freethreading-devel as a component of Red Hat Enterprise Linux 10; python3.14-freethreading-idle as a component of Red Hat Enterprise Linux 10; python3.14-freethreading-libs as a component of Red Hat Enterprise Linux 10; python3.14-freethreading-test as a component of Red Hat Enterprise Linux 10; python3.14-freethreading-tkinter as a component of Red Hat Enterprise Linux 10; python3.14-idle as a component of Red Hat Enterprise Linux 10; python3.14-libs as a component of Red Hat Enterprise Linux 10; python3.14-test as a component of Red Hat Enterprise Linux 10; python3.14-tkinter as a component of Red Hat Enterprise Linux 10; python3.14.src as a component of Red Hat Enterprise Linux 10; python3.14 as a component of Red Hat Enterprise Linux 9; python3.14-debug as a component of Red Hat Enterprise Linux 9; python3.14-devel as a component of Red Hat Enterprise Linux 9; python3.14-freethreading as a component of Red Hat Enterprise Linux 9; python3.14-freethreading-debug as a component of Red Hat Enterprise Linux 9; python3.14-freethreading-devel as a component of Red Hat Enterprise Linux 9; python3.14-freethreading-idle as a component of Red Hat Enterprise Linux 9; python3.14-freethreading-libs as a component of Red Hat Enterprise Linux 9; python3.14-freethreading-test as a component of Red Hat Enterprise Linux 9; python3.14-freethreading-tkinter as a component of Red Hat Enterprise Linux 9; python3.14-idle as a component of Red Hat Enterprise Linux 9; python3.14-libs as a component of Red Hat Enterprise Linux 9; python3.14-test as a component of Red Hat Enterprise Linux 9; python3.14-tkinter as a component of Red Hat Enterprise Linux 9; python3.14.src as a component of Red Hat Enterprise Linux 9; and 1 more · Fixed: python3-12-main@aarch64 as a component of Red Hat Hardened Images; python3-12-main@src as a component of Red Hat Hardened Images; python3-12-main@x86_64 as a component of Red Hat Hardened Images; python3-13-main@aarch64 as a component of Red Hat Hardened Images; python3-13-main@src as a component of Red Hat Hardened Images; python3-13-main@x86_64 as a component of Red Hat Hardened Images; python3-14-main@aarch64 as a component of Red Hat Hardened Images; python3-14-main@noarch as a component of Red Hat Hardened Images; python3-14-main@src as a component of Red Hat Hardened Images; python3-14-main@x86_64 as a component of Red Hat Hardened Images
After
python3.14 as a component of Red Hat Enterprise Linux 10; python3.14-debug as a component of Red Hat Enterprise Linux 10; python3.14-devel as a component of Red Hat Enterprise Linux 10; python3.14-freethreading as a component of Red Hat Enterprise Linux 10; python3.14-freethreading-debug as a component of Red Hat Enterprise Linux 10; python3.14-freethreading-devel as a component of Red Hat Enterprise Linux 10; python3.14-freethreading-idle as a component of Red Hat Enterprise Linux 10; python3.14-freethreading-libs as a component of Red Hat Enterprise Linux 10; python3.14-freethreading-test as a component of Red Hat Enterprise Linux 10; python3.14-freethreading-tkinter as a component of Red Hat Enterprise Linux 10; python3.14-idle as a component of Red Hat Enterprise Linux 10; python3.14-libs as a component of Red Hat Enterprise Linux 10; python3.14-test as a component of Red Hat Enterprise Linux 10; python3.14-tkinter as a component of Red Hat Enterprise Linux 10; python3.14.src as a component of Red Hat Enterprise Linux 10; python3.14 as a component of Red Hat Enterprise Linux 9; python3.14-debug as a component of Red Hat Enterprise Linux 9; python3.14-devel as a component of Red Hat Enterprise Linux 9; python3.14-freethreading as a component of Red Hat Enterprise Linux 9; python3.14-freethreading-debug as a component of Red Hat Enterprise Linux 9; python3.14-freethreading-devel as a component of Red Hat Enterprise Linux 9; python3.14-freethreading-idle as a component of Red Hat Enterprise Linux 9; python3.14-freethreading-libs as a component of Red Hat Enterprise Linux 9; python3.14-freethreading-test as a component of Red Hat Enterprise Linux 9; python3.14-freethreading-tkinter as a component of Red Hat Enterprise Linux 9; python3.14-idle as a component of Red Hat Enterprise Linux 9; python3.14-libs as a component of Red Hat Enterprise Linux 9; python3.14-test as a component of Red Hat Enterprise Linux 9; python3.14-tkinter as a component of Red Hat Enterprise Linux 9; python3.14.src as a component of Red Hat Enterprise Linux 9 · Fixed: python3-11-main@aarch64 as a component of Red Hat Hardened Images; python3-11-main@src as a component of Red Hat Hardened Images; python3-11-main@x86_64 as a component of Red Hat Hardened Images; python3-12-main@aarch64 as a component of Red Hat Hardened Images; python3-12-main@src as a component of Red Hat Hardened Images; python3-12-main@x86_64 as a component of Red Hat Hardened Images; python3-13-main@aarch64 as a component of Red Hat Hardened Images; python3-13-main@src as a component of Red Hat Hardened Images; python3-13-main@x86_64 as a component of Red Hat Hardened Images; python3-14-main@aarch64 as a component of Red Hat Hardened Images; python3-14-main@noarch as a component of Red Hat Hardened Images; python3-14-main@src as a component of Red Hat Hardened Images; python3-14-main@x86_64 as a component of Red Hat Hardened Images
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
CVE-2026-3446: Base64 decoding stops at first padded quad by default | BlackTree
