protobufjs: Text Format string map parsing can mutate returned map object prototype

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

protobufjs compiles protobuf definitions into JavaScript (JS) functions. From 8.2.0 until 8.6.5, the protobufjs Text Format extension parsed string-keyed map entries using ordinary property assignment, allowing a map entry with key __proto__ to change the prototype of the returned map object instead of creating an own map entry in protobufjs/ext/textformat. This issue is fixed in version 8.6.5.

Source published

8 Jul 2026 15:31:11 UTC

Source modified

9 Jul 2026 14:41:45 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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CVSS 3.1 · 4.8 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

protobufjs compiles protobuf definitions into JavaScript (JS) functions. From 8.2.0 until 8.6.5, the protobufjs Text Format extension parsed string-keyed map entries using ordinary property assignment, allowing a map entry with key __proto__ to change the prototype of the returned map object instead of creating an own map entry in protobufjs/ext/textformat. This issue is fixed in version 8.6.5.

Source published

Jul 8, 2026, 3:31:11 PM (timezone not stated)

Source modified

Jul 9, 2026, 2:41:45 PM (timezone not stated)

Observed here

7 Nov 2026 13:25:56 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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EUVD CVSS 3.1 · 4.8 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

protobufjs compiles protobuf definitions into JavaScript (JS) functions. From 8.2.0 until 8.6.5, the protobufjs Text Format extension parsed string-keyed map entries using ordinary property assignment, allowing a map entry with key __proto__ to change the prototype of the returned map object instead of creating an own map entry in protobufjs/ext/textformat. This issue is fixed in version 8.6.5.

Source published

8 Jul 2026 16:16:34 UTC

Source modified

25 Oct 2026 17:10:00 UTC

Observed here

27 Oct 2026 15:15:33 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 4.8 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

CVSS 3.1 · [email protected] · Primary · 4.8 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

## Summary The protobuf.js text format extension parsed string-keyed map entries using ordinary property assignment. A text-format map entry with key `__proto__` could therefore change the prototype of the returned map object instead of creating an own map entry. This affected the optional Text Format extension. Other protobufjs input paths, including binary decode, `fromObject`, and ProtoJSON conversion, are not affected. ## Impact An attacker who can provide protobuf text-format input parsed by an application using `protobufjs/ext/textformat` may be able to create message objects whose string-keyed map fields have attacker-controlled prototypes. This is per-object prototype mutation, not global `Object.prototype` pollution. Impact depends on downstream application logic treating inherited properties as meaningful, for example by using `in`, truthiness checks, or direct property access on parsed map objects instead of own-property checks. Applications that do not parse untrusted Text Format input, or that do not use inherited properties from parsed map objects in security-relevant logic, are not directly affected. ## Preconditions * The application must parse attacker-controlled protobuf Text Format input with `protobufjs/ext/textformat`. * The target schema must contain a string-keyed map field. * The crafted input must provide a map entry with key `__proto__`. * Downstream application logic must treat inherited properties on the returned map object as meaningful for impact beyond malformed output. ## Workarounds Upgrade to protobufjs 8.6.5 or newer. If immediate upgrade is not possible, do not parse untrusted protobuf Text Format input with affected versions. Applications can also reject string map keys named `__proto__` before or during Text Format parsing, and should use own-property checks such as `Object.hasOwnProperty.call(map, key)` when consuming parsed map objects.

Source published

20 Jul 2026 22:04:07 UTC

Source modified

10 Sep 2026 03:50:12 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

Publisher rating · MODERATE