Cgo directive injection via .syso files disguised as Go object files in cmd/go and cmd/link

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

not scored

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

Building a package containing a crafted ".syso" file could bypass cgo flag validation and inject arbitrary linker flags when linking. When loading ".syso" entries from a package archive, the linker only checked for recognized host object headers (ELF, Mach-O, PE, and XCOFF) before falling through to Go object parsing. A ".syso" file beginning with a "go object" header was parsed as a Go compiler object, allowing untrusted cgo metadata directives (such as "cgo_ldflag" or "cgo_dynamic_linker") embedded in the ".syso" file to be passed to the external linker without validation. Additionally, ".syso" filenames longer than 16 bytes lost their ".syso" extension when truncated in archive headers, and unrecognized ".syso" formats forced external linking in pure-Go builds. The linker now rejects ".syso" files that are not recognized host object formats, and "cmd/go" and "cmd/pack" preserve the ".syso" suffix when truncating long archive member names.

Published by the source

11 Nov 2026, 02:51 UTC

Last modified by the source

11 Nov 2026, 03:15 UTC

Source last checked

11 Nov 2026, 07:20 UTC

1. Revision 1 · created · 11 Nov 2026

   Published from osv record GO-2026-6851

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# Patch Next advisory brief: CVE-2026-97040

Advisory: Cgo directive injection via .syso files disguised as Go object files in cmd/go and cmd/link
IDs: CVE-2026-97040
Record: https://patchnext.com/advisories/cve-2026-97040 (revision 1, source checked 11 Nov 2026, 07:20 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Unrated
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: toolchain 1.27.4, 1.26.11. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go toolchain: affected < 1.26.11; >= 1.27.0-0, < 1.27.4; fixed in 1.26.11, 1.27.4

## Suggested inspection (read-only)
- Go toolchain: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on toolchain.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GO-2026-6851 (OSV record GO-2026-6851 lists affected ranges: Go toolchain >=0 =1.27.0-0 <1.27.4 (fixed))

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