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Response snapshot Oct 31, 2026, 02:31 UTC

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VulnerabilityCVE-2026-117656

Acceptance of Extraneous Untrusted Data With Trusted Data vulnerability in the Sign in with Apple strategy in pow-auth Assent allows an unauthenticated remote attacker to...

Acceptance of Extraneous Untrusted Data With Trusted Data vulnerability in the Sign in with Apple strategy in pow-auth Assent allows an unauthenticated remote attacker to impersonate another user via the user parameter of the authorization callback.

At a glance

Exploited
Not known
Severity
9.3 Critical (CVSS 4.0)
Chance of exploitation
Not estimated
Sources
1 source

What to do

Check the vendor advisory for affected versions and fixes.

Read NVD CVE-2026-117656 (opens a new tab)

What happened

Acceptance of Extraneous Untrusted Data With Trusted Data vulnerability in the Sign in with Apple strategy in pow-auth Assent allows an unauthenticated remote attacker to impersonate another user via the user parameter of the authorization callback.

Apple posts the user's name to the callback endpoint in a user form parameter that the browser submits and the client controls. Assent.Strategy.Apple.callback/2 in lib/assent/strategies/apple.ex decodes that parameter, and fetch_user/2 merges it over the claims of the verified ID token, so the unverified map wins.

An attacker who completes a Sign in with Apple login with their own Apple ID and edits the user parameter can replace sub, email, and any other claim. Applications that look up, link, or authorize accounts by the returned subject or email then act on the attacker's values.

This issue affects assent: from 0.1.25 before 0.3.2.

Scores and how they were measured

CVSS base severity

9.3

Version 4.0As of

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/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

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

Not available

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Sources

  1. Primary source

    NVD CVE-2026-117656 (opens a new tab)

    NVD record: description, CVSS (the CNA score is preferred), affected products, and publication date. Not evidence of exploitation.

    Published Checked

  2. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  3. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 31). Acceptance of Extraneous Untrusted Data With Trusted Data vulnerability in the Sign in with Apple strategy in pow-auth Assent allows an unauthenticated remote attacker to... (CVE-2026-117656). https://kevwire.com/record/CVE-2026-117656

MLA

"Acceptance of Extraneous Untrusted Data With Trusted Data vulnerability in the Sign in with Apple strategy in pow-auth Assent allows an unauthenticated remote attacker to... (CVE-2026-117656)." KEVWire, 31 Oct. 2026, kevwire.com/record/CVE-2026-117656.

Chicago

KEVWire. "Acceptance of Extraneous Untrusted Data With Trusted Data vulnerability in the Sign in with Apple strategy in pow-auth Assent allows an unauthenticated remote attacker to... (CVE-2026-117656)." Last modified October 31, 2026. https://kevwire.com/record/CVE-2026-117656.

Evidence summary (plain text)

Acceptance of Extraneous Untrusted Data With Trusted Data vulnerability in the Sign in with Apple strategy in pow-auth Assent allows an unauthenticated remote attacker to... (Oct 31, 2026).
Acceptance of Extraneous Untrusted Data With Trusted Data vulnerability in the Sign in with Apple strategy in pow-auth Assent allows an unauthenticated remote attacker to impersonate another user via the user parameter of the authorization callback.

Apple posts the user's name to the callback endpoint in a user form parameter that the browser submits and the client controls. Assent.Strategy.Apple.callback/2 in lib/assent/strategies/apple.ex decodes that parameter, and fetch_user/2 merges it over the claims of the verified ID token, so the unverified map wins.
CVSS 9.3 (version 4.0; evidence as of Oct 31, 2026; https://nvd.nist.gov/vuln/detail/CVE-2026-117656).
Sources:
NVD CVE-2026-117656: https://nvd.nist.gov/vuln/detail/CVE-2026-117656
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-10-30T23:50:58.706Z&lastModEndDate=2026-10-31T01:25:58.327Z&resultsPerPage=500&startIndex=0
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-10-30T23:16:04.425Z&lastModEndDate=2026-10-31T00:50:55.911Z&resultsPerPage=500&startIndex=0
Record ID: CVE-2026-117656.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 31, 2026, 01:25 UTC. Ingestion is not an independent editorial investigation.

NVD status: Received. Publication in the NVD is not evidence of exploitation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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Record details

Record detail