Partial update overwrite

PATCH and JSON merge behavior that overwrites read-only, derived, or financial fields when only a subset of fields should change.

1 phút đọccập nhật 2 thg 10, 2026

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Context#

PATCH is not uniform across frameworks: JSON Merge Patch, custom shallow merge, and null to delete semantics differ. A client can intend to change name while the merge overwrites balance or role if those keys are accepted in the merge input object.

Theory#

The same mass-assignment class appears when the operation is “partial” but the object shape is the full model. null and absent key often mean different things; attackers probe both.

Practice#

Send full document shape with one extra sensitive key#

In a lab, take a GET of the object, copy the JSON, add a creditLimit or status key that should be server-only, and PATCH it. Compare the next GET.

Tools#

curl
Burp Suite