plugin: restrict characters in plugin names

Thanks to ⬡-49016 for reporting this issue.

Fixes GHSA-32gq-x56h-299c

cmd/age/testdata/plugin.txt

@@ -10,6 +10,15 @@ age -d -i long-key.txt test.age
 cmp stdout input
 ! stderr .
 
+# check that path separators are rejected
+chmod 755 age-plugin-pwn/pwn
+mkdir $TMPDIR/age-plugin-pwn
+cp age-plugin-pwn/pwn $TMPDIR/age-plugin-pwn/pwn
+! age -r age1pwn/pwn19gt89dfz input
+! age -d -i pwn-identity.txt test.age
+! age -d -j pwn/pwn test.age
+! exists pwn
+
 -- input --
 test
 -- key.txt --
@@ -18,3 +27,8 @@ AGE-PLUGIN-TEST-10Q32NLXM
 age1test10pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7rc0pu8s7qj6rl8p
 -- long-key.txt --
 AGE-PLUGIN-TEST-10PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7RC0PU8S7Q5U8SUD
+-- pwn-identity.txt --
+AGE-PLUGIN-PWN/PWN-19GYK4WLY
+-- age-plugin-pwn/pwn --
+#!/bin/sh
+touch "$WORK/pwn"

plugin/client.go

@@ -15,6 +15,7 @@ import (
 	"os"
 	"path/filepath"
 	"strconv"
+	"strings"
 	"time"
 
 	exec "golang.org/x/sys/execabs"
@@ -178,6 +179,9 @@ func NewIdentity(s string, ui *ClientUI) (*Identity, error) {
 
 func NewIdentityWithoutData(name string, ui *ClientUI) (*Identity, error) {
 	s := EncodeIdentity(name, nil)
+	if s == "" {
+		return nil, fmt.Errorf("invalid plugin name: %q", name)
+	}
 	return &Identity{
 		name: name, encoding: s, ui: ui,
 	}, nil
@@ -390,6 +394,8 @@ func openClientConnection(name, protocol string) (*clientConnection, error) {
 	path := "age-plugin-" + name
 	if testOnlyPluginPath != "" {
 		path = filepath.Join(testOnlyPluginPath, path)
+	} else if strings.ContainsRune(name, os.PathSeparator) {
+		return nil, fmt.Errorf("invalid plugin name: %q", name)
 	}
 	cmd := exec.Command(path, "--age-plugin="+protocol)
 

plugin/encode.go

@@ -14,6 +14,9 @@ import (
 // EncodeIdentity encodes a plugin identity string for a plugin with the given
 // name. If the name is invalid, it returns an empty string.
 func EncodeIdentity(name string, data []byte) string {
+	if !validPluginName(name) {
+		return ""
+	}
 	s, _ := bech32.Encode("AGE-PLUGIN-"+strings.ToUpper(name)+"-", data)
 	return s
 }
@@ -30,12 +33,18 @@ func ParseIdentity(s string) (name string, data []byte, err error) {
 	}
 	name = strings.TrimSuffix(strings.TrimPrefix(hrp, "AGE-PLUGIN-"), "-")
 	name = strings.ToLower(name)
+	if !validPluginName(name) {
+		return "", nil, fmt.Errorf("invalid plugin name: %q", name)
+	}
 	return name, data, nil
 }
 
 // EncodeRecipient encodes a plugin recipient string for a plugin with the given
 // name. If the name is invalid, it returns an empty string.
 func EncodeRecipient(name string, data []byte) string {
+	if !validPluginName(name) {
+		return ""
+	}
 	s, _ := bech32.Encode("age1"+strings.ToLower(name), data)
 	return s
 }
@@ -51,5 +60,21 @@ func ParseRecipient(s string) (name string, data []byte, err error) {
 		return "", nil, fmt.Errorf("not a plugin recipient: %v", err)
 	}
 	name = strings.TrimPrefix(hrp, "age1")
+	if !validPluginName(name) {
+		return "", nil, fmt.Errorf("invalid plugin name: %q", name)
+	}
 	return name, data, nil
 }
+
+func validPluginName(name string) bool {
+	if name == "" {
+		return false
+	}
+	allowed := "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789+-._"
+	for _, r := range name {
+		if !strings.ContainsRune(allowed, r) {
+			return false
+		}
+	}
+	return true
+}