Unexpected code execution and arbitrary file write via Clang -gen-* and GCC -gnat* flags in cgo in cmd/go

published 2026-11-11 yesterday modified 2026-11-11 yesterday also EUVD-2026-123110 , GO-2026-6856

cvss: —; not scored
cisa kev: Not listed; not in CISA's catalog
epss: 0.3%; EPSS 0.3% chance of exploitation in 30 days, percentile 16%
public exploits: 0; none known

When using Clang or GCC, building a malicious package that uses cgo could cause unexpected code execution at build time or write files to arbitrary directories via "-gen-*" or "-gnat*" flags in "#cgo" directives. The "-g*" wildcard in the compiler and linker flag allowlists previously matched Clang's two-argument "-gen-cdb-fragment-path <dir>" flag and GCC's two-argument "-gnatO <file>" flag, permitting compilation database fragments and sidecar output files to be written to arbitrary directories and desynchronizing flag argument parsing between the go command and the compiler driver so that subsequent arguments could be passed as unvalidated positional inputs to the linker. "-gen-*" and "-gnat*" flags are now disallowed in "#cgo" compiler and linker flags.

Patch / fix

fixed in 2 links 1

go toolchain 1.26.11, 1.27.4
Go toolchain cmd/go 1.26.11, 1.27.4

go.dev/cl/862148 patch

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Exploit prediction

0.25% chance of exploitation in the next 30 days, higher than 16% of all scored CVEs (FIRST EPSS, 2026-11-11).

Affected packages

ecosystem	package	affected	fixed in
go	toolchain	<1.26.11 >=1.27.0-0, <1.27.4	1.26.11 1.27.4

Affected products

Go toolchain cmd/go

Classification

Weakness

CWE-88 Improper Neutralization of Argument Delimiters in a Command

References

go.dev /cl/862148
patch
go.dev /issue/82575
report
groups.google.com /g/golang-announce/c/iY8TY0wWgbM
web
pkg.go.dev /vuln/GO-2026-6856

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.