CVE-2026-45820: Fflate Fflate UnzipSync Can Enter An Vulnerability
MODERATECVE-2026-45820 is a MODERATE (CVSS 7.5) fflate unzipsync can enter an vulnerability (CWE-400: Uncontrolled Resource Consumption) affecting Fflate libraries in the npm ecosystem. The issue involves fflate unzipsync can enter an infinite loop when parsing malformed zip64 archives. Remediation is available by upgrading affected packages to version 0.4.9, 0.5.4, 0.6.11, 0.7.5, 0.8.3.
CVE-2026-45820 at a Glance
Security Impact
CVSS: 7.5
The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).
How to Fix CVE-2026-45820
To remediate this vulnerability, upgrade all affected Fflate dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.
npm install fflate@0.4.9npm install fflate@0.5.4npm install fflate@0.6.11npm install fflate@0.7.5npm install fflate@0.8.3Run the following command in your project directory to verify that all resolved dependencies use the patched release:
npm ls fflateHow to Check if You Are Affected
To determine whether your Node.js application is affected by CVE-2026-45820, inspect your project dependencies using npm:
npm ls fflateAnalyze the terminal output to locate any version of Fflate in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 0.4.9), your application is affected.
Note: The npm ls fflate command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.
Technical Details
Vulnerability Mechanism & Technical Analysis
This vulnerability is classified under CWE-400: Uncontrolled Resource Consumption, where the product does not properly control the allocation and maintenance of a limited resource. In Fflate, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.
Source Advisory Statement
CVE-2026-45820 Affected Fflate Versions
5 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
fflate
|
npm |
≥ 0.4.5
< 0.4.9
|
0.4.9
|
|
fflate
|
npm |
≥ 0.5.0
< 0.5.4
|
0.5.4
|
|
fflate
|
npm |
≥ 0.6.0
< 0.6.11
|
0.6.11
|
|
fflate
|
npm |
≥ 0.7.0
< 0.7.5
|
0.7.5
|
|
fflate
|
npm |
≥ 0.8.0
< 0.8.3
|
0.8.3
|
References
Frequently Asked Questions
What is CVE-2026-45820?
Which Fflate versions are affected?
What version fixes CVE-2026-45820?
Is fflate affected?
What is the CVSS score of CVE-2026-45820?
What CWE is associated with CVE-2026-45820?
How can I check npm dependencies for CVE-2026-45820?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-px8p-9vwx-vf98",
"modified" : "2026-09-03T14:58:12Z",
"published" : "2026-07-22T09:32:13Z",
"aliases" : [ "CVE-2026-45820" ],
"summary" : "fflate unzipSync can enter an infinite loop when parsing malformed ZIP64 archives",
"details" : "fflate through 0.8.2 is vulnerable to denial of service via an infinite loop in unzipSync(). A crafted ZIP archive with a central directory entry declaring compressed_size=0xFFFFFFFF (ZIP64 sentinel) but missing the required ZIP64 extra field tag 0x0001 causes z64e() to loop indefinitely due to out-of-bounds reads returning undefined, which coerces to 0, keeping the loop condition permanently true.",
"severity" : [ {
"type" : "CVSS_V3",
"score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
}, {
"type" : "CVSS_V4",
"score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/S:N/AU:Y/R:U/V:D/RE:M/U:Amber"
} ],
"affected" : [ {
"package" : {
"ecosystem" : "npm",
"name" : "fflate"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0.4.5"
}, {
"fixed" : "0.4.9"
} ]
} ]
}, {
"package" : {
"ecosystem" : "npm",
"name" : "fflate"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0.5.0"
}, {
"fixed" : "0.5.4"
} ]
} ]
}, {
"package" : {
"ecosystem" : "npm",
"name" : "fflate"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0.6.0"
}, {
"fixed" : "0.6.11"
} ]
} ]
}, {
"package" : {
"ecosystem" : "npm",
"name" : "fflate"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0.7.0"
}, {
"fixed" : "0.7.5"
} ]
} ]
}, {
"package" : {
"ecosystem" : "npm",
"name" : "fflate"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0.8.0"
}, {
"fixed" : "0.8.3"
} ]
} ]
} ],
"references" : [ {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-45820"
}, {
"type" : "WEB",
"url" : "https://github.com/101arrowz/fflate/commit/e6d5e6e1076892f72770ac732d83c81da9f3316e"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/101arrowz/fflate"
}, {
"type" : "WEB",
"url" : "https://github.com/101arrowz/fflate/blob/f7873560ad229c22c4b23b06c6a3806ffde77569/src/index.ts#L2714"
}, {
"type" : "WEB",
"url" : "https://github.com/101arrowz/fflate/releases/tag/v0.8.3"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-400" ],
"severity" : "MODERATE",
"github_reviewed" : true,
"github_reviewed_at" : "2026-09-03T14:58:12Z",
"nvd_published_at" : "2026-07-22T08:16:23Z"
}
}