diff --git a/VolumeManager.cpp b/VolumeManager.cpp
index 757fae7..1ffa939 100644
--- a/VolumeManager.cpp
+++ b/VolumeManager.cpp
@@ -211,6 +211,12 @@
 int VolumeManager::getAsecMountPath(const char *id, char *buffer, int maxlen) {
     char asecFileName[255];
 
+    if (!isLegalAsecId(id)) {
+        SLOGE("getAsecMountPath: Invalid asec id \"%s\"", id);
+        errno = EINVAL;
+        return -1;
+    }
+
     if (findAsec(id, asecFileName, sizeof(asecFileName))) {
         SLOGE("Couldn't find ASEC %s", id);
         return -1;
@@ -235,6 +241,12 @@
 int VolumeManager::getAsecFilesystemPath(const char *id, char *buffer, int maxlen) {
     char asecFileName[255];
 
+    if (!isLegalAsecId(id)) {
+        SLOGE("getAsecFilesystemPath: Invalid asec id \"%s\"", id);
+        errno = EINVAL;
+        return -1;
+    }
+
     if (findAsec(id, asecFileName, sizeof(asecFileName))) {
         SLOGE("Couldn't find ASEC %s", id);
         return -1;
@@ -260,6 +272,12 @@
     struct asec_superblock sb;
     memset(&sb, 0, sizeof(sb));
 
+    if (!isLegalAsecId(id)) {
+        SLOGE("createAsec: Invalid asec id \"%s\"", id);
+        errno = EINVAL;
+        return -1;
+    }
+
     const bool wantFilesystem = strcmp(fstype, "none");
     bool usingExt4 = false;
     if (wantFilesystem) {
@@ -483,6 +501,12 @@
     char loopDevice[255];
     char mountPoint[255];
 
+    if (!isLegalAsecId(id)) {
+        SLOGE("finalizeAsec: Invalid asec id \"%s\"", id);
+        errno = EINVAL;
+        return -1;
+    }
+
     if (findAsec(id, asecFileName, sizeof(asecFileName))) {
         SLOGE("Couldn't find ASEC %s", id);
         return -1;
@@ -540,6 +564,12 @@
         return -1;
     }
 
+    if (!isLegalAsecId(id)) {
+        SLOGE("fixupAsecPermissions: Invalid asec id \"%s\"", id);
+        errno = EINVAL;
+        return -1;
+    }
+
     if (findAsec(id, asecFileName, sizeof(asecFileName))) {
         SLOGE("Couldn't find ASEC %s", id);
         return -1;
@@ -659,6 +689,18 @@
 
     const char *dir;
 
+    if (!isLegalAsecId(id1)) {
+        SLOGE("renameAsec: Invalid asec id1 \"%s\"", id1);
+        errno = EINVAL;
+        return -1;
+    }
+
+    if (!isLegalAsecId(id2)) {
+        SLOGE("renameAsec: Invalid asec id2 \"%s\"", id2);
+        errno = EINVAL;
+        return -1;
+    }
+
     if (findAsec(id1, asecFilename1, sizeof(asecFilename1), &dir)) {
         SLOGE("Couldn't find ASEC %s", id1);
         return -1;
@@ -715,6 +757,12 @@
     char asecFileName[255];
     char mountPoint[255];
 
+    if (!isLegalAsecId(id)) {
+        SLOGE("unmountAsec: Invalid asec id \"%s\"", id);
+        errno = EINVAL;
+        return -1;
+    }
+
     if (findAsec(id, asecFileName, sizeof(asecFileName))) {
         SLOGE("Couldn't find ASEC %s", id);
         return -1;
@@ -839,6 +887,12 @@
     char asecFileName[255];
     char mountPoint[255];
 
+    if (!isLegalAsecId(id)) {
+        SLOGE("destroyAsec: Invalid asec id \"%s\"", id);
+        errno = EINVAL;
+        return -1;
+    }
+
     if (findAsec(id, asecFileName, sizeof(asecFileName))) {
         SLOGE("Couldn't find ASEC %s", id);
         return -1;
@@ -871,6 +925,38 @@
     return 0;
 }
 
+/*
+ * Legal ASEC ids consist of alphanumeric characters, '-',
+ * '_', or '.'. ".." is not allowed. The first or last character
+ * of the ASEC id cannot be '.' (dot).
+ */
+bool VolumeManager::isLegalAsecId(const char *id) const {
+    size_t i;
+    size_t len = strlen(id);
+
+    if (len == 0) {
+        return false;
+    }
+    if ((id[0] == '.') || (id[len - 1] == '.')) {
+        return false;
+    }
+
+    for (i = 0; i < len; i++) {
+        if (id[i] == '.') {
+            // i=0 is guaranteed never to have a dot. See above.
+            if (id[i-1] == '.') return false;
+            continue;
+        }
+        if (id[i] == '_' || id[i] == '-') continue;
+        if (id[i] >= 'a' && id[i] <= 'z') continue;
+        if (id[i] >= 'A' && id[i] <= 'Z') continue;
+        if (id[i] >= '0' && id[i] <= '9') continue;
+        return false;
+    }
+
+    return true;
+}
+
 bool VolumeManager::isAsecInDirectory(const char *dir, const char *asecName) const {
     int dirfd = open(dir, O_DIRECTORY);
     if (dirfd < 0) {
@@ -895,6 +981,12 @@
     const int idLen = strlen(id);
     char *asecName;
 
+    if (!isLegalAsecId(id)) {
+        SLOGE("findAsec: Invalid asec id \"%s\"", id);
+        errno = EINVAL;
+        return -1;
+    }
+
     if (asprintf(&asecName, "%s.asec", id) < 0) {
         SLOGE("Couldn't allocate string to write ASEC name");
         return -1;
@@ -931,6 +1023,12 @@
     char asecFileName[255];
     char mountPoint[255];
 
+    if (!isLegalAsecId(id)) {
+        SLOGE("mountAsec: Invalid asec id \"%s\"", id);
+        errno = EINVAL;
+        return -1;
+    }
+
     if (findAsec(id, asecFileName, sizeof(asecFileName))) {
         SLOGE("Couldn't find ASEC %s", id);
         return -1;
diff --git a/VolumeManager.h b/VolumeManager.h
index 9d69d6a..cc8958d 100644
--- a/VolumeManager.h
+++ b/VolumeManager.h
@@ -154,6 +154,7 @@
     void readInitialState();
     bool isMountpointMounted(const char *mp);
     bool isAsecInDirectory(const char *dir, const char *asec) const;
+    bool isLegalAsecId(const char *id) const;
 };
 
 extern "C" {