diff --git a/GPU/Common/PostShader.cpp b/GPU/Common/PostShader.cpp
index 0603a25d08..26539321fe 100644
--- a/GPU/Common/PostShader.cpp
+++ b/GPU/Common/PostShader.cpp
@@ -31,6 +31,7 @@
 #include "Common/StringUtils.h"
 
 #include "Core/System.h"
+#include "Core/Util/PathUtil.h"
 #include "GPU/Common/PostShader.h"
 
 static std::vector<ShaderInfo> shaderInfo;
@@ -154,12 +155,17 @@ void LoadPostShaderInfo(Draw::DrawContext *draw, const std::vector<Path> &direct
 					section.Get("Name", &info.name);
 					section.Get("Parent", &info.parent);
 					section.Get("Visible", &info.visible);
-					temp.clear();
-					section.Get("Fragment", &temp);
-					info.fragmentShaderFile = path / temp;
-					temp.clear();
-					section.Get("Vertex", &temp);
-					info.vertexShaderFile = path / temp;
+					std::string fragment;
+					std::string vertex;
+					section.Get("Fragment", &fragment);
+					section.Get("Vertex", &vertex);
+					// Shader inis come from downloads, so keep them to their own folder.
+					if (HasParentDirComponent(fragment) || HasParentDirComponent(vertex)) {
+						WARN_LOG(Log::G3D, "Ignoring shader '%s' with a parent dir in its paths", info.section.c_str());
+						continue;
+					}
+					info.fragmentShaderFile = path / fragment;
+					info.vertexShaderFile = path / vertex;
 					section.Get("OutputResolution", &info.outputResolution);
 					section.Get("Upscaling", &info.isUpscalingFilter);
 					section.Get("SSAA", &info.SSAAFilterLevel);
@@ -221,19 +227,33 @@ void LoadPostShaderInfo(Draw::DrawContext *draw, const std::vector<Path> &direct
 					section.Get("Hidden", &info.hidden);
 					std::string cbufferFilename;
 					if (section.Get("ConstantBuffer", &cbufferFilename)) {
+						if (HasParentDirComponent(cbufferFilename)) {
+							WARN_LOG(Log::G3D, "Ignoring texture shader '%s' with a parent dir in its paths", info.section.c_str());
+							continue;
+						}
 						Path cbufferPath = path / cbufferFilename;
 						info.constantBuffer = cbufferPath;
 					}
 					if (section.Get("Compute", &temp)) {
+						if (HasParentDirComponent(temp)) {
+							WARN_LOG(Log::G3D, "Ignoring texture shader '%s' with a parent dir in its paths", info.section.c_str());
+							continue;
+						}
 						info.computeShaderFile = path / temp;
 						info.computeShaderFiles.push_back(info.computeShaderFile);
+						bool badPath = false;
 						for (int computeIndex = 2; computeIndex <= 4; ++computeIndex) {
 							temp.clear();
 							if (section.Get(StringFromFormat("Compute%d", computeIndex).c_str(), &temp)) {
+								if (HasParentDirComponent(temp)) {
+									badPath = true;
+								}
 								info.computeShaderFiles.push_back(path / temp);
 							}
 						}
-						if (info.scaleFactor >= 2 && info.scaleFactor < 8) {
+						if (badPath) {
+							WARN_LOG(Log::G3D, "Ignoring texture shader '%s' with a parent dir in its paths", info.section.c_str());
+						} else if (info.scaleFactor >= 2 && info.scaleFactor < 8) {
 							appendTextureShader(info);
 						}
 					} else {
diff --git a/GPU/Common/ReplacedTexture.cpp b/GPU/Common/ReplacedTexture.cpp
index 6a77d4b698..1ff28e5753 100644
--- a/GPU/Common/ReplacedTexture.cpp
+++ b/GPU/Common/ReplacedTexture.cpp
@@ -1015,9 +1015,21 @@ bool ReplacedTexture::CopyLevelTo(int level, uint8_t *out, size_t outDataSize, i
 		WARN_LOG(Log::TexReplacement, "Level %d is empty", level);
 		return false;
 	}
+	if (info.w > outW || info.h > outH) {
+		WARN_LOG(Log::TexReplacement, "Level %d (%dx%d) is bigger than its padded size %dx%d", level, info.w, info.h, outW, outH);
+		return false;
+	}
 
 	int blockSize;
-	if (!Draw::DataFormatIsBlockCompressed(fmt, &blockSize)) {
+	const bool blockCompressed = Draw::DataFormatIsBlockCompressed(fmt, &blockSize);
+	const size_t needed = blockCompressed ? (size_t)((outW + 3) / 4) * ((outH + 3) / 4) * blockSize : (size_t)rowPitch * (outH - 1) + outW * 4;
+	// A zero size disables the check, like for the other copies.
+	if (outDataSize != 0 && outDataSize < needed) {
+		WARN_LOG(Log::TexReplacement, "Level %d doesn't fit the buffer (%d < %d)", level, (int)outDataSize, (int)needed);
+		return false;
+	}
+
+	if (!blockCompressed) {
 		if (fmt != Draw::DataFormat::R8G8B8A8_UNORM) {
 			ERROR_LOG(Log::TexReplacement, "Unexpected linear data format");
 			return false;
diff --git a/GPU/Common/TextureReplacer.cpp b/GPU/Common/TextureReplacer.cpp
index b143de8e11..96087d883e 100644
--- a/GPU/Common/TextureReplacer.cpp
+++ b/GPU/Common/TextureReplacer.cpp
@@ -413,8 +413,9 @@ bool TextureReplacer::LoadIniValues(IniFile &ini, VFSBackend *dir, bool isOverri
 			std::string_view v = line.Value();
 			if (sscanf(k, "%16llx%8x_%d", &key.cachekey, &key.hash, &level) >= 1) {
 				// Reject path traversal: a "../" component could make us read
-				// or write files outside the texture pack directory.
-				if (HasParentDirComponent(v)) {
+				// or write files outside the texture pack directory. '|' separates mip levels in the alias,
+				// so it would let a later level skip this check.
+				if (HasParentDirComponent(v) || v.find('|') != std::string_view::npos) {
 					ERROR_LOG(Log::TexReplacement, "Ignoring texture filename with parent dir component: %s", std::string(v).c_str());
 					continue;
 				}
@@ -521,6 +522,12 @@ void TextureReplacer::ParseHashRange(const std::string &key, const std::string &
 		return;
 	}
 
+	// Generous, PSP textures are at most 512x512. Values of 65536 or more would also spill into the other fields of the key.
+	if (fromW > 1024 || fromH > 1024) {
+		ERROR_LOG(Log::TexReplacement, "Ignoring invalid hashrange %s = %s, source bigger than 1024x1024", key.c_str(), value.c_str());
+		return;
+	}
+
 	if (toW > fromW || toH > fromH) {
 		ERROR_LOG(Log::TexReplacement, "Ignoring invalid hashrange %s = %s, range bigger than source", key.c_str(), value.c_str());
 		return;
@@ -934,13 +941,13 @@ void TextureReplacer::NotifyTextureDecoded(ReplacedTexture *texture, const Repla
 	// Only save the hashed portion of the PNG, in case we have specified it in the ini file.
 	int lookupW;
 	int lookupH;
-	if (LookupHashRange(replacedInfo.addr, origW, origH, &lookupW, &lookupH)) {
+	if (LookupHashRange(replacedInfo.addr, origW, origH, &lookupW, &lookupH) && lookupW > 0 && lookupH > 0 && lookupW <= origW && lookupH <= origH) {
 		w = lookupW * (scaledW / origW);
 		h = lookupH * (scaledH / origH);
 	}
 
 	constexpr int bpp = 4;
-	size_t saveBufSize = w * h * bpp;
+	size_t saveBufSize = (size_t)w * h * bpp;
 	u8 *saveBuf = (u8 *)malloc(saveBufSize);
 	if (!saveBuf) {
 		ERROR_LOG(Log::TexReplacement, "Failed to allocated %d bytes of memory for saving a texture", (int)saveBufSize);
@@ -950,7 +957,7 @@ void TextureReplacer::NotifyTextureDecoded(ReplacedTexture *texture, const Repla
 	// Copy data to a buffer so we can send it to the thread. Might as well compact-away the pitch
 	// while we're at it.
 	for (int y = 0; y < h; y++) {
-		memcpy(saveBuf + y * w * bpp, (const u8 *)data + y * srcPitch, w * bpp);
+		memcpy(saveBuf + (size_t)y * w * bpp, (const u8 *)data + (size_t)y * srcPitch, w * bpp);
 	}
 
 	SaveTextureTask *task = new SaveTextureTask(std::move(saveBuf));
diff --git a/GPU/Vulkan/TextureCacheVulkan.cpp b/GPU/Vulkan/TextureCacheVulkan.cpp
index 1b07e163ae..1df467ec60 100644
--- a/GPU/Vulkan/TextureCacheVulkan.cpp
+++ b/GPU/Vulkan/TextureCacheVulkan.cpp
@@ -366,6 +366,13 @@ bool TextureCacheVulkan::LoadConstantBuffer(VulkanContext *vulkan, VkCommandBuff
 		ClearScalingShaders(vulkan);
 		return false;
 	}
+	// The file comes with a downloaded shader, and has to make a valid uniform buffer.
+	if (constantsSize < 16 || (constantsSize & 15) != 0 || constantsSize > vulkan->GetPhysicalDeviceProperties().properties.limits.maxUniformBufferRange) {
+		ERROR_LOG(Log::G3D, "Constant buffer file '%s' has a bad size (%d) - disabling hardware scaling", cbufferPath_.c_str(), (int)constantsSize);
+		delete[] contents;
+		ClearScalingShaders(vulkan);
+		return false;
+	}
 	textureScaleCBuffer_.Create(vulkan, "TextureScale CBuffer", constantsSize, VK_BUFFER_USAGE_UNIFORM_BUFFER_BIT | VK_BUFFER_USAGE_TRANSFER_DST_BIT);
 	VulkanPushPool *pushPool = drawEngine_->GetPushBufferForTextureData();
 	VkBuffer srcBuf = VK_NULL_HANDLE;