Bug 2521870 (CVE-2026-76845)

Summary: CVE-2026-76845 adm-zip: adm-zip: Arbitrary File Overwrite via Symlink Following
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: abarbaro, akhatavk, alizardo, aos-team-art-private, asdas, cdrage, dpaolell, dschmidt, gbenhaim, gmalinko, gparvin, janstey, jchui, jdelft, jhe, jlanda, jupierce, kshier, ktsao, lgarciaa, mbiarnes, nboldt, niyer, oaljalju, pdelbell, ppalepu, ppostler, prdhamdh, psrna, rhaigner, rhel-process-autobot, rstepani, rushinde, sghai, sidsharm, simaishi, stcannon, suppawar, teagle, twaugh, vlaad, watson-tool-maintainers, yguenane
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in `adm-zip`, a Node.js library used for handling zip archives. This vulnerability allows a local attacker to overwrite arbitrary files on the system. When extracting an archive, `adm-zip` follows symbolic links, which are special files that point to other files or directories. An attacker can exploit this by placing a symbolic link within a temporary extraction directory, redirecting the extraction process to write data outside the intended secure location. This could lead to unauthorized modification of system files.
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Description OSIDB Bzimport 2026-08-24 13:22:54 UTC 
adm-zip 0.5.9 through 0.6.0 follows symbolic links at the extraction destination. Utils.sanitize in util/utils.js enforces containment by comparing only the string form of an archive entry name against the resolved extraction root, and Utils.writeFileTo opens the computed destination with fs.openSync(path, "w", 0o666), which resolves symbolic links and carries neither O_NOFOLLOW nor a pre-write fs.lstatSync check. When a path component at the destination already exists as a symbolic link pointing outside the extraction root, extractAllTo, extractAllToAsync and extractEntryTo write the entry contents through that link and then chmod its target, placing attacker-controlled content in a file outside the root without any traversal sequence appearing in the archive. Reaching the write requires overwrite to be enabled, because the preceding fs.existsSync check also resolves the link and otherwise declines. An attacker able to create a symbolic link inside a shared, reused or predictable extraction directory, such as a temporary directory or a continuous integration workspace, can overwrite any file the extracting process is permitted to write.