{"resultsPerPage":1,"startIndex":0,"totalResults":1,"format":"NVD_CVE","version":"2.0","timestamp":"2026-06-03T13:25:49.666","vulnerabilities":[{"cve":{"id":"CVE-2025-12781","sourceIdentifier":"cna@python.org","published":"2026-01-21T20:16:04.423","lastModified":"2026-02-02T17:25:23.933","vulnStatus":"Analyzed","cveTags":[],"descriptions":[{"lang":"en","value":"When passing data to the b64decode(), standard_b64decode(), and urlsafe_b64decode() functions in the \"base64\" module the characters \"+/\" will always be accepted, regardless of the value of \"altchars\" parameter, typically used to establish an \"alternative base64 alphabet\" such as the URL safe alphabet. This behavior matches what is recommended in earlier base64 RFCs, but newer RFCs now recommend either dropping characters outside the specified base64 alphabet or raising an error. The old behavior has the possibility of causing data integrity issues.\n\n\n\n\nThis behavior can only be insecure if your application uses an alternate base64 alphabet (without \"+/\"). If your application does not use the \"altchars\" parameter or the urlsafe_b64decode() function, then your application does not use an alternative base64 alphabet.\n\n\n\n\nThe attached patches DOES NOT make the base64-decode behavior raise an error, as this would be a change in behavior and break existing programs. Instead, the patch deprecates the behavior which will be replaced with the newly recommended behavior in a future version of Python. Users are recommended to mitigate by verifying user-controlled inputs match the base64 \nalphabet they are expecting or verify that their application would not be \naffected if the b64decode() functions accepted \"+\" or \"/\" outside of altchars."},{"lang":"es","value":"Al pasar datos a las funciones b64decode(), standard_b64decode() y urlsafe_b64decode() en el módulo \"base64\", los caracteres \"+/\" siempre serán aceptados, independientemente del valor del parámetro \"altchars\", típicamente usado para establecer un 'alfabeto base64 alternativo' como el alfabeto seguro para URL. Este comportamiento coincide con lo recomendado en RFCs de base64 anteriores, pero los RFCs más recientes ahora recomiendan o bien descartar caracteres fuera del alfabeto base64 especificado o generar un error. El comportamiento antiguo tiene la posibilidad de causar problemas de integridad de datos.\n\nEste comportamiento solo puede ser inseguro si su aplicación usa un alfabeto base64 alternativo (sin \"+/\"). Si su aplicación no usa el parámetro \"altchars\" o la función urlsafe_b64decode(), entonces su aplicación no usa un alfabeto base64 alternativo.\n\nLos parches adjuntos NO hacen que el comportamiento de decodificación base64 genere un error, ya que esto sería un cambio de comportamiento y rompería programas existentes. En su lugar, el parche desaprueba el comportamiento que será reemplazado por el comportamiento recién recomendado en una futura versión de Python. Se recomienda a los usuarios mitigar verificando que las entradas controladas por el usuario coincidan con el alfabeto base64 que esperan o verificar que su aplicación no se vería afectada si las funciones b64decode() aceptaran \"+\" o \"/\" fuera de altchars."}],"metrics":{"cvssMetricV40":[{"source":"cna@python.org","type":"Secondary","cvssData":{"version":"4.0","vectorString":"CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/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","baseScore":6.3,"baseSeverity":"MEDIUM","attackVector":"NETWORK","attackComplexity":"HIGH","attackRequirements":"PRESENT","privilegesRequired":"NONE","userInteraction":"NONE","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"LOW","vulnAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","subAvailabilityImpact":"NONE","exploitMaturity":"NOT_DEFINED","confidentialityRequirement":"NOT_DEFINED","integrityRequirement":"NOT_DEFINED","availabilityRequirement":"NOT_DEFINED","modifiedAttackVector":"NOT_DEFINED","modifiedAttackComplexity":"NOT_DEFINED","modifiedAttackRequirements":"NOT_DEFINED","modifiedPrivilegesRequired":"NOT_DEFINED","modifiedUserInteraction":"NOT_DEFINED","modifiedVulnConfidentialityImpact":"NOT_DEFINED","modifiedVulnIntegrityImpact":"NOT_DEFINED","modifiedVulnAvailabilityImpact":"NOT_DEFINED","modifiedSubConfidentialityImpact":"NOT_DEFINED","modifiedSubIntegrityImpact":"NOT_DEFINED","modifiedSubAvailabilityImpact":"NOT_DEFINED","Safety":"NOT_DEFINED","Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","valueDensity":"NOT_DEFINED","vulnerabilityResponseEffort":"NOT_DEFINED","providerUrgency":"NOT_DEFINED"}}],"cvssMetricV31":[{"source":"nvd@nist.gov","type":"Primary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","baseScore":5.3,"baseSeverity":"MEDIUM","attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"NONE","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"NONE","integrityImpact":"LOW","availabilityImpact":"NONE"},"exploitabilityScore":3.9,"impactScore":1.4}]},"weaknesses":[{"source":"134c704f-9b21-4f2e-91b3-4a467353bcc0","type":"Secondary","description":[{"lang":"en","value":"CWE-704"}]}],"configurations":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:a:python:python:*:*:*:*:*:*:*:*","versionEndExcluding":"3.13.10","matchCriteriaId":"B02C195C-8271-4207-9FE9-E46C7A4978AE"},{"vulnerable":true,"criteria":"cpe:2.3:a:python:python:*:*:*:*:*:*:*:*","versionStartIncluding":"3.14.0","versionEndExcluding":"3.14.1","matchCriteriaId":"6E66BA7A-987F-4E24-8B69-4F46D6FCD19E"},{"vulnerable":true,"criteria":"cpe:2.3:a:python:python:3.15.0:alpha1:*:*:*:*:*:*","matchCriteriaId":"A3327507-0B1D-4F28-A983-D07A2C8A7696"}]}]}],"references":[{"url":"https://github.com/python/cpython/commit/13360efd385d1a7d0659beba03787ea3d063ef9b","source":"cna@python.org","tags":["Patch"]},{"url":"https://github.com/python/cpython/commit/1be80bec7960f5ccd059e75f3dfbd45fca302947","source":"cna@python.org","tags":["Patch"]},{"url":"https://github.com/python/cpython/commit/9060b4abbe475591b6230b23c2afefeff26fcca5","source":"cna@python.org","tags":["Patch"]},{"url":"https://github.com/python/cpython/commit/e95e783dff443b68e8179fdb57737025bf02ba76","source":"cna@python.org","tags":["Patch"]},{"url":"https://github.com/python/cpython/commit/fd17ee026fa9b67f6288cbafe374a3e479fe03a5","source":"cna@python.org","tags":["Patch"]},{"url":"https://github.com/python/cpython/issues/125346","source":"cna@python.org","tags":["Exploit","Issue Tracking"]},{"url":"https://github.com/python/cpython/pull/141128","source":"cna@python.org","tags":["Issue Tracking","Patch"]},{"url":"https://mail.python.org/archives/list/security-announce@python.org/thread/KRI7GC6S27YV5NJ4FPDALS2WI5ENAFJ6/","source":"cna@python.org","tags":["Mailing List","Vendor Advisory"]}]}}]}