What’s Vulnerable › Vulnerabilities

CVE-2026-93753: deepmerge through 4.3.1 Prototype Poisoning via mergeObject

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-18 · updated 2026-09-23
• Weakness: CWE-1321

Description

deepmerge through 4.3.1 contains a prototype poisoning vulnerability in the mergeObject() function that fails to properly validate keys being written to target objects. Attackers can supply malicious source objects in merge operations to inject attacker-controlled properties into the returned object's prototype, causing applications to inherit unintended values when accessing properties without own-property checks.

Affected products

• TehShrike deepmerge: through 4.3.1

References

• https://github.com/TehShrike/deepmerge
• https://github.com/TehShrike/deepmerge/blob/5b87756a5671635679001cbac72aa42f23472c81/index.js#L39-L60
• https://github.com/TehShrike/deepmerge/issues/273
• https://www.vulncheck.com/advisories/deepmerge-through-4.3.1-prototype-poisoning-via-mergeobject
• https://github.com/TehShrike/deepmerge/issues/273

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