diff --git a/apps/server/AliasVault.Api/Controllers/AuthController.cs b/apps/server/AliasVault.Api/Controllers/AuthController.cs
index 4a660acdb..48d2880ba 100644
--- a/apps/server/AliasVault.Api/Controllers/AuthController.cs
+++ b/apps/server/AliasVault.Api/Controllers/AuthController.cs
@@ -110,10 +110,11 @@ public class AuthController(IAliasServerDbContextFactory dbContextFactory, UserM
 
                 if (AppInfo.MinimumClientVersions.TryGetValue(platform, out var minimumVersion))
                 {
-                    if (VersionHelper.IsVersionEqualOrNewer(clientVersion, minimumVersion))
-                    {
-                        clientSupported = true;
-                    }
+                    // Check if version meets minimum requirement AND is not in blocked list
+                    var meetsMinimum = VersionHelper.IsVersionEqualOrNewer(clientVersion, minimumVersion);
+                    var isBlocked = VersionHelper.IsVersionBlocked(platform, clientVersion, AppInfo.UnsupportedClientVersions);
+
+                    clientSupported = meetsMinimum && !isBlocked;
                 }
                 else
                 {
diff --git a/apps/server/AliasVault.Api/Helpers/VersionHelper.cs b/apps/server/AliasVault.Api/Helpers/VersionHelper.cs
index 5f2f6d4b6..34bcd8c93 100644
--- a/apps/server/AliasVault.Api/Helpers/VersionHelper.cs
+++ b/apps/server/AliasVault.Api/Helpers/VersionHelper.cs
@@ -59,4 +59,36 @@ public static class VersionHelper
         // Compare the versions
         return v1 >= v2;
     }
+
+    /// <summary>
+    /// Checks if a version is blocked for a specific platform.
+    /// Checks both platform-specific blocks and global blocks (using "*" key).
+    /// </summary>
+    /// <param name="platform">The platform to check (e.g., "chrome", "ios").</param>
+    /// <param name="version">The version to check.</param>
+    /// <param name="blockedVersions">Dictionary of platform to blocked versions. Use "*" for global blocks.</param>
+    /// <returns>True if the version is blocked for this platform, false otherwise.</returns>
+    public static bool IsVersionBlocked(string platform, string version, IReadOnlyDictionary<string, HashSet<string>> blockedVersions)
+    {
+        if (string.IsNullOrEmpty(version) || blockedVersions == null || blockedVersions.Count == 0)
+        {
+            return false;
+        }
+
+        // Check global blocks (applies to all platforms)
+        if (blockedVersions.TryGetValue("*", out var globalBlocked) && globalBlocked.Contains(version))
+        {
+            return true;
+        }
+
+        // Check platform-specific blocks
+        if (!string.IsNullOrEmpty(platform) &&
+            blockedVersions.TryGetValue(platform, out var platformBlocked) &&
+            platformBlocked.Contains(version))
+        {
+            return true;
+        }
+
+        return false;
+    }
 }
diff --git a/apps/server/Shared/AliasVault.Shared.Core/AppInfo.cs b/apps/server/Shared/AliasVault.Shared.Core/AppInfo.cs
index c78e9cb95..d79fc7b41 100644
--- a/apps/server/Shared/AliasVault.Shared.Core/AppInfo.cs
+++ b/apps/server/Shared/AliasVault.Shared.Core/AppInfo.cs
@@ -42,7 +42,7 @@ public static class AppInfo
     /// for all clients as we are using a monorepo to build all clients from the same source code. But it's
     /// possible to override the minimum client version for a specific client if needed.
     /// </summary>
-    public const string MinimumClientVersion = "0.26.1";
+    public const string MinimumClientVersion = "0.12.0";
 
     /// <summary>
     /// Gets a dictionary of minimum supported client versions that the WebApi supports.
@@ -68,6 +68,24 @@ public static class AppInfo
         { "android", MinimumClientVersion },
     }.AsReadOnly();
 
+    /// <summary>
+    /// Gets a dictionary of specific client versions that are explicitly unsupported (blocked) per platform.
+    /// This is useful for blocking specific versions with (critical) bugs while still allowing
+    /// older versions that predate the bug to continue working.
+    /// For example: if 0.26.0 has a critical bug fixed in 0.26.1, we can block only 0.26.0
+    /// without affecting users on 0.25.x who may still have compatible vaults.
+    /// Use "*" as the platform key to block a version across all platforms.
+    /// </summary>
+    public static IReadOnlyDictionary<string, HashSet<string>> UnsupportedClientVersions { get; } = new Dictionary<string, HashSet<string>>
+    {
+        // Block version across all platforms: "*" applies to all clients.
+        { "*", ["0.26.0"] }, // Version with vault migration bug, fixed in 0.26.1
+
+        // Platform-specific blocks (examples):
+        // { "chrome", ["0.25.0"] },
+        // { "ios", ["0.24.0", "0.24.1"] },
+    };
+
     /// <summary>
     /// Gets the build number, typically used in CI/CD pipelines.
     /// Can be overridden at build time.
diff --git a/apps/server/Tests/AliasVault.UnitTests/Vault/VersionTests.cs b/apps/server/Tests/AliasVault.UnitTests/Vault/VersionTests.cs
index 0b3685858..fb4fef0cc 100644
--- a/apps/server/Tests/AliasVault.UnitTests/Vault/VersionTests.cs
+++ b/apps/server/Tests/AliasVault.UnitTests/Vault/VersionTests.cs
@@ -68,4 +68,96 @@ public class VersionTests
         var version2 = "1.1.0";
         Assert.That(VersionHelper.IsVersionEqualOrNewer(version1, version2), Is.True);
     }
+
+    /// <summary>
+    /// Test that a version in the global blocked list is correctly identified as blocked.
+    /// </summary>
+    [Test]
+    public void VersionBlockedReturnsTrueForGloballyBlockedVersion()
+    {
+        var blockedVersions = new Dictionary<string, HashSet<string>>
+        {
+            { "*", ["0.26.0", "0.27.0"] },
+        };
+
+        Assert.That(VersionHelper.IsVersionBlocked("chrome", "0.26.0", blockedVersions), Is.True);
+        Assert.That(VersionHelper.IsVersionBlocked("ios", "0.27.0", blockedVersions), Is.True);
+        Assert.That(VersionHelper.IsVersionBlocked("android", "0.26.0", blockedVersions), Is.True);
+    }
+
+    /// <summary>
+    /// Test that a version in the platform-specific blocked list is correctly identified as blocked.
+    /// </summary>
+    [Test]
+    public void VersionBlockedReturnsTrueForPlatformSpecificBlockedVersion()
+    {
+        var blockedVersions = new Dictionary<string, HashSet<string>>
+        {
+            { "chrome", ["0.25.0"] },
+            { "ios", ["0.24.0"] },
+        };
+
+        // Platform-specific blocks should work
+        Assert.That(VersionHelper.IsVersionBlocked("chrome", "0.25.0", blockedVersions), Is.True);
+        Assert.That(VersionHelper.IsVersionBlocked("ios", "0.24.0", blockedVersions), Is.True);
+
+        // Other platforms should not be blocked
+        Assert.That(VersionHelper.IsVersionBlocked("firefox", "0.25.0", blockedVersions), Is.False);
+        Assert.That(VersionHelper.IsVersionBlocked("android", "0.24.0", blockedVersions), Is.False);
+    }
+
+    /// <summary>
+    /// Test that global and platform-specific blocks work together.
+    /// </summary>
+    [Test]
+    public void VersionBlockedCombinesGlobalAndPlatformSpecific()
+    {
+        var blockedVersions = new Dictionary<string, HashSet<string>>
+        {
+            { "*", ["0.26.0"] },
+            { "chrome", ["0.25.0"] },
+        };
+
+        // Global block applies to all platforms for exact version
+        Assert.That(VersionHelper.IsVersionBlocked("chrome", "0.26.0", blockedVersions), Is.True);
+        Assert.That(VersionHelper.IsVersionBlocked("ios", "0.26.0", blockedVersions), Is.True);
+        Assert.That(VersionHelper.IsVersionBlocked("ios", "0.26.1", blockedVersions), Is.False);
+
+        // Platform-specific block only applies to that platform
+        Assert.That(VersionHelper.IsVersionBlocked("chrome", "0.25.0", blockedVersions), Is.True);
+        Assert.That(VersionHelper.IsVersionBlocked("firefox", "0.25.0", blockedVersions), Is.False);
+    }
+
+    /// <summary>
+    /// Test that a version not in the blocked list is correctly identified as not blocked.
+    /// </summary>
+    [Test]
+    public void VersionBlockedReturnsFalseForNonBlockedVersion()
+    {
+        var blockedVersions = new Dictionary<string, HashSet<string>>
+        {
+            { "*", ["0.26.0"] },
+        };
+
+        Assert.That(VersionHelper.IsVersionBlocked("chrome", "0.25.3", blockedVersions), Is.False);
+        Assert.That(VersionHelper.IsVersionBlocked("chrome", "0.26.1", blockedVersions), Is.False);
+        Assert.That(VersionHelper.IsVersionBlocked("chrome", "0.27.0", blockedVersions), Is.False);
+    }
+
+    /// <summary>
+    /// Test that empty or null inputs are handled correctly.
+    /// </summary>
+    [Test]
+    public void VersionBlockedHandlesEmptyInputs()
+    {
+        var blockedVersions = new Dictionary<string, HashSet<string>>
+        {
+            { "*", ["0.26.0"] },
+        };
+
+        var emptyBlockedVersions = new Dictionary<string, HashSet<string>>();
+
+        Assert.That(VersionHelper.IsVersionBlocked("chrome", string.Empty, blockedVersions), Is.False);
+        Assert.That(VersionHelper.IsVersionBlocked("chrome", "0.26.0", emptyBlockedVersions), Is.False);
+    }
 }