[AutoPR- Security] Patch packer for CVE-2026-19589 [HIGH]

[Azure Linux Security Servicing Account (azurelinux-security)]

Auto Patch packer for CVE-2026-19589.

Autosec pipeline run -> https://dev.azure.com/mariner-org/mariner/_build/results?buildId=1185585&view=results

CVE-2026-19589 : Single Patch Backporter Pipeline Run -> https://dev.azure.com/mariner-org/mariner/_build/results?buildId=1185590&view=results

Merge Checklist

All boxes should be checked before merging the PR (just tick any boxes which don't apply to this PR)

• The toolchain has been rebuilt successfully (or no changes were made to it)
• The toolchain/worker package manifests are up-to-date
• Any updated packages successfully build (or no packages were changed)
• Packages depending on static components modified in this PR (Golang, *-static subpackages, etc.) have had their Release tag incremented.
• Package tests (%check section) have been verified with RUN_CHECK=y for existing SPEC files, or added to new SPEC files
• All package sources are available
• cgmanifest files are up-to-date and sorted (./cgmanifest.json, ./toolkit/scripts/toolchain/cgmanifest.json, .github/workflows/cgmanifest.json)
• LICENSE-MAP files are up-to-date (./LICENSES-AND-NOTICES/SPECS/data/licenses.json, ./LICENSES-AND-NOTICES/SPECS/LICENSES-MAP.md, ./LICENSES-AND-NOTICES/SPECS/LICENSE-EXCEPTIONS.PHOTON)
• All source files have up-to-date hashes in the *.signatures.json files
• sudo make go-tidy-all and sudo make go-test-coverage pass
• Documentation has been updated to match any changes to the build system
• Ready to merge

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Summary

What does the PR accomplish, why was it needed?

• Auto Patch packer for CVE-2026-19589 (HIGH).

Change Log

• CVE-2026-19589

Does this affect the toolchain?

YES/NO

Associated issues

• N/A

Links to CVEs

• https://nvd.nist.gov/vuln/detail/CVE-2026-19589

Test Methodology

• Pipeline build id: Buddy Build URL

[azure-pipelines]

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[v-swapsahu]

Patch Analysis:
CVE-2026-19589
Backported: Yes

Issue: When installing a plugin, Packer trusted the filename listed in the remote SHA256SUMS file to decide where to write the binary. A malicious release using a name like packer-plugin-docker_v1.2.3_x5.0_linux_amd64/../../tmp/PWNED.zip_ causes Packer to write outside the plugin directory → arbitrary file write.

Affected: Azure Linux ships packer 1.9.5 → affected. Upstream fix da95976 targets code that doesn't exist verbatim in 1.9.5, so it is backported.

Root cause: In plugins.go::InstallLatest, the entry is parsed/validated but the code then used the raw checksum.Filename to build outputFileName = filepath.Join(outputFolder, ...), so ../ escapes the folder at os.OpenFile().

Fix:
Rebuild the filename from the already-validated entry fields instead of the raw name, via a new Getter.ExpectedFileName(...) method — same design as upstream. Two adaptations were required for 1.9.5:

• pr.Identifier.Type instead of upstream's pr.Identifier.Source (1.9.5 addrs.Plugin has no Source field).
• Exported accessors entry.BinVersion()/ProtVersion()/Os()/Arch()/Ext() instead of upstream's exported struct fields (1.9.5 fields are unexported).

Testing: Upstream's scenario test is in getter_test.go (absent from Azure source) and %check doesn't run the plugin-getter package, so no test is shipped.

Verification is done out-of-band via a standalone POC that drives the real InstallLatest with a malicious checksum entry and asserts nothing is written outside the install folder:

• Unpatched 1.9.5 → FAILS (writes …/hashicorp/PWNED, escaping the plugin dir).

• With the backport → PASSES (safe filename rebuilt; nothing escapes).

Patch Application:

Local Build have been passed:

[Kanishk Bansal (Kanishk-Bansal)]

/azurepipelines run

[azure-pipelines]

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