diff --git a/include/znc/HTTPSock.h b/include/znc/HTTPSock.h
index ca3e737a..d2b2edd4 100644
--- a/include/znc/HTTPSock.h
+++ b/include/znc/HTTPSock.h
@@ -52,6 +52,10 @@ class CHTTPSock : public CSocket {
                      unsigned int uStatusId = 200,
                      const CString& sStatusMsg = "OK");
     void AddHeader(const CString& sName, const CString& sValue);
+    /** Returns false if `s` contains CR or LF. Used by AddHeader to reject
+     * inputs that could split the response into a separate header or body
+     * (RFC 7230 disallows obs-fold; treat any bare CR/LF as invalid). */
+    static bool IsValidHeaderField(const CString& s);
     void SetContentType(const CString& sContentType);
 
     bool PrintNotFound();
diff --git a/src/HTTPSock.cpp b/src/HTTPSock.cpp
index 237713e6..2ff3a643 100644
--- a/src/HTTPSock.cpp
+++ b/src/HTTPSock.cpp
@@ -762,7 +762,17 @@ void CHTTPSock::SetContentType(const CString& sContentType) {
     m_sContentType = sContentType;
 }
 
+bool CHTTPSock::IsValidHeaderField(const CString& s) {
+    return s.find_first_of("\r\n") == CString::npos;
+}
+
 void CHTTPSock::AddHeader(const CString& sName, const CString& sValue) {
+    // Reject CR/LF in either half so we never emit a malformed header or
+    // give a caller (e.g. a future module) a cheap response-splitting
+    // primitive. No in-tree caller reaches this with attacker-controlled
+    // bytes today; this is a defensive guard, not a fix for an existing
+    // exploit.
+    if (!IsValidHeaderField(sName) || !IsValidHeaderField(sValue)) return;
     m_msHeaders[sName] = sValue;
 }
 
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 92f4f621..f928dc83 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -61,7 +61,7 @@ add_executable(unittest_bin EXCLUDE_FROM_ALL
 	"ThreadTest.cpp" "NickTest.cpp" "ClientTest.cpp" "NetworkTest.cpp"
 	"MessageTest.cpp" "ModulesTest.cpp" "IRCSockTest.cpp" "QueryTest.cpp"
 	"StringTest.cpp" "ConfigTest.cpp" "BufferTest.cpp" "UtilsTest.cpp"
-	"UserTest.cpp" "DebugTest.cpp")
+	"UserTest.cpp" "DebugTest.cpp" "HTTPSockTest.cpp")
 target_link_libraries(unittest_bin PRIVATE znclib)
 target_include_directories(unittest_bin PRIVATE
 	"${GTEST_ROOT}" "${GTEST_ROOT}/include"
diff --git a/test/HTTPSockTest.cpp b/test/HTTPSockTest.cpp
new file mode 100644
index 00000000..420d847b
--- /dev/null
+++ b/test/HTTPSockTest.cpp
@@ -0,0 +1,39 @@
+/*
+ * Copyright (C) 2004-2026 ZNC, see the NOTICE file for details.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <gtest/gtest.h>
+#include <znc/HTTPSock.h>
+
+// Validation contract used by AddHeader to keep CR/LF (and therefore
+// response-splitting bytes) out of the response stream (#2010).
+TEST(HTTPSockTest, IsValidHeaderField) {
+    // Plain field names and values are accepted.
+    EXPECT_TRUE(CHTTPSock::IsValidHeaderField(""));
+    EXPECT_TRUE(CHTTPSock::IsValidHeaderField("X-Custom"));
+    EXPECT_TRUE(CHTTPSock::IsValidHeaderField("text/html; charset=utf-8"));
+    EXPECT_TRUE(CHTTPSock::IsValidHeaderField("a value with spaces and tabs\t"));
+
+    // CR or LF anywhere is rejected; both halves of a CRLF pair are
+    // rejected even individually.
+    EXPECT_FALSE(CHTTPSock::IsValidHeaderField("\r"));
+    EXPECT_FALSE(CHTTPSock::IsValidHeaderField("\n"));
+    EXPECT_FALSE(CHTTPSock::IsValidHeaderField("\r\n"));
+    EXPECT_FALSE(CHTTPSock::IsValidHeaderField("X\rFoo"));
+    EXPECT_FALSE(CHTTPSock::IsValidHeaderField("X\nFoo"));
+    EXPECT_FALSE(CHTTPSock::IsValidHeaderField("safe\r\nInjected: yes"));
+    EXPECT_FALSE(CHTTPSock::IsValidHeaderField("trailing\n"));
+    EXPECT_FALSE(CHTTPSock::IsValidHeaderField("\rleading"));
+}