adm-zip before 0.6.1 Duplicate ZIP Entry Name Validation Bypass

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.

adm-zip before 0.6.1 contains an inconsistent entry resolution vulnerability that allows attackers to bypass content validation by supplying ZIP archives with duplicate entry names. Attackers can craft archives where getEntry() returns the last duplicate while extractAllTo() writes the first, causing unvalidated bytes to be written to disk.

Source published

21 Oct 2026 00:37:05 UTC

Source modified

28 Oct 2026 16:14:55 UTC

Observed here

28 Oct 2026 17:46:48 UTC

Source terms

CVE Program Terms of Use

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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: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · 8.2 CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

CVSS 3.1 · 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

adm-zip before 0.6.1 contains an inconsistent entry resolution vulnerability that allows attackers to bypass content validation by supplying ZIP archives with duplicate entry names. Attackers can craft archives where getEntry() returns the last duplicate while extractAllTo() writes the first, causing unvalidated bytes to be written to disk.

Source published

Oct 21, 2026, 12:37:05 AM (timezone not stated)

Source modified

Oct 28, 2026, 4:14:55 PM (timezone not stated)

Observed here

30 Oct 2026 01:58:35 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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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: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 4.0 · 8.2 CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

adm-zip before 0.6.1 contains an inconsistent entry resolution vulnerability that allows attackers to bypass content validation by supplying ZIP archives with duplicate entry names. Attackers can craft archives where getEntry() returns the last duplicate while extractAllTo() writes the first, causing unvalidated bytes to be written to disk.

Source published

21 Oct 2026 01:17:36 UTC

Source modified

28 Oct 2026 17:17:47 UTC

Observed here

29 Oct 2026 06:48:04 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 4.0 · [email protected] · Secondary · 8.2 CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

CVSS 3.1 · [email protected] · Secondary · 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

### Summary A ZIP file can contain two entries with the identical name. adm-zip keeps both in its internal entry list, but its name-lookup table only retains the last one written. `getEntry(name)` and `extractAllTo()` walk these two different internal structures, so they can each resolve a duplicate name to a *different* entry. An application that validates a named entry's contents via `getEntry()` before trusting an archive, then extracts the whole archive, can end up approving one file's content while a different file's bytes are what actually land on disk under that name. ### Details - `zipFile.js:58-83` retains both entries in `entryList` but overwrites `entryTable[name]` with only the last one written. - `adm-zip.js:83-95,658-663` uses `entryTable` for `getEntry()` lookups — returns the *last* duplicate. - `adm-zip.js:769-914` iterates `entryList` for extraction — writes the *first* duplicate (sync, default overwrite policy). ### PoC ```js const AdmZip = require('adm-zip'); const z = new AdmZip({ noSort: true }); z.addFile('a.txt', Buffer.from('FIRST')); z.addFile('b.txt', Buffer.from('SECOND')); const raw = Buffer.from(z.toBuffer()); // rename the a.txt entry to b.txt directly in the raw bytes for (let at = raw.indexOf('a.txt'); at >= 0; at = raw.indexOf('a.txt', at + 5)) { raw.write('b.txt', at); } const parsed = new AdmZip(raw, { noSort: true }); const validated = parsed.getEntry('b.txt').getData().toString(); parsed.extractAllTo(outDir, false); // validated === "SECOND", but the file written to disk === "FIRST" ``` Reproduced on the pinned commit (`2b4d84087d45344643e0183756e19191d52815cc`) ### Impact An application that checks a named entry's content before trusting an untrusted ZIP, then extracts it, can be made to approve different bytes than what actually gets written to disk — the classic check/use split that this kind of validate-then-extract pattern relies on.

Source published

29 Sep 2026 23:11:01 UTC

Source modified

21 Oct 2026 10:57:22 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:N/I:H/A:N

Publisher rating · MODERATE