From 945b935ac66cc7f1a41f1b849c7c25adb5351f49 Mon Sep 17 00:00:00 2001
From: Igor Ustinov <igus68@gmail.com>
Date: Thu, 5 Mar 2026 15:47:34 +0100
Subject: [PATCH] Avoid possible buffer overflow in buf2hex conversion
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Fixes CVE-2026-31789

Reviewed-by: Saša Nedvědický <sashan@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.foundation>
MergeDate: Mon Apr  6 19:39:23 2026
(cherry picked from commit 3244aa4b9d6ea0220cc14fd97d951c67b5052837)
---
 crypto/o_str.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/crypto/o_str.c b/crypto/o_str.c
index 35540630be25f..9b9e7751fdd9e 100644
--- a/crypto/o_str.c
+++ b/crypto/o_str.c
@@ -296,6 +296,11 @@ static int buf2hexstr_sep(char *str, size_t str_n, size_t *strlength,
     int has_sep = (sep != CH_ZERO);
     size_t i, len = has_sep ? buflen * 3 : 1 + buflen * 2;
 
+    if (buflen > (has_sep ? SIZE_MAX / 3 : (SIZE_MAX - 1) / 2)) {
+        ERR_raise(ERR_LIB_CRYPTO, CRYPTO_R_TOO_MANY_BYTES);
+        return 0;
+    }
+
     if (len == 0)
         ++len;
     if (strlength != NULL)
@@ -339,7 +344,13 @@ char *ossl_buf2hexstr_sep(const unsigned char *buf, long buflen, char sep)
     if (buflen == 0)
         return OPENSSL_zalloc(1);
 
-    tmp_n = (sep != CH_ZERO) ? buflen * 3 : 1 + buflen * 2;
+    if ((sep != CH_ZERO && (size_t)buflen > SIZE_MAX / 3)
+        || (sep == CH_ZERO && (size_t)buflen > (SIZE_MAX - 1) / 2)) {
+        ERR_raise(ERR_LIB_CRYPTO, CRYPTO_R_TOO_MANY_BYTES);
+        return NULL;
+    }
+
+    tmp_n = (sep != CH_ZERO) ? (size_t)buflen * 3 : 1 + (size_t)buflen * 2;
     if ((tmp = OPENSSL_malloc(tmp_n)) == NULL)
         return NULL;
 
