Remote Prototype Pollution in i18next-http-middleware missingKeyHandler
CVE-2026-48714 is a prototype pollution vulnerability in i18next-http-middleware affecting versions prior to 3.9.7. The flaw is in missingKeyHandler: although the middleware blocked literal request-body keys such as proto, constructor, and prototype beginning in 3.9.3, it failed to reject dotted variants such as "proto.polluted". When such attacker-controlled keys are forwarded to downstream backends that split missing-key strings using a configured keySeparator, notably i18next-fs-backend <= 2.6.5, they can reach an unguarded setPath()-style walker and cause writes to Object.prototype. In deployments that expose missingKeyHandler to untrusted input, this creates a remotely exploitable prototype pollution condition.
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Exploits
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Recent activity
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A companion middleware vulnerability that expands the attack surface and helps remote input reach the vulnerable code path associated with the i18next-fs-backend prototype pollution issue.
A critical remote prototype pollution vulnerability in i18next-http-middleware's missingKeyHandler that can allow untrusted input to write to Object.prototype via dotted keys, especially when used with i18next-fs-backend 2.6.5 or earlier.
The version that knows your environment.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.