From e894699c1ea4a5e4cf0256fc9eba05a754ab1e58 Mon Sep 17 00:00:00 2001
From: Daniel Stenberg <daniel@haxx.se>
Date: Tue, 17 Mar 2026 13:23:30 +0100
Subject: [PATCH] strerr: correct the strerror_s() return code condition

In curlx_strerror on Windows, the condition checks `!strerror_s(...)`
(true on success) and therefore always evaluates the fallback block.
Even when strerror_s successfully produced a valid errno message.

Follow-up to 1eca08a54177403205014

Pointed out by Codex Security
Closes #20955
---
 lib/curlx/strerr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/curlx/strerr.c b/lib/curlx/strerr.c
index 91a329e915..b53173c578 100644
--- a/lib/curlx/strerr.c
+++ b/lib/curlx/strerr.c
@@ -263,7 +263,7 @@ const char *curlx_strerror(int err, char *buf, size_t buflen)
   *buf = '\0';
 
 #ifdef _WIN32
-  if((!strerror_s(buf, buflen, err) || !strcmp(buf, "Unknown error")) &&
+  if((strerror_s(buf, buflen, err) || !strcmp(buf, "Unknown error")) &&
 #ifdef USE_WINSOCK
      !get_winsock_error(err, buf, buflen) &&
 #endif