CVE-2021-32762: Integer Overflow to Buffer Overflow (CWE-680)
value: Redis is an open source, in-memory database that persists on disk. The redis-cli command line tool and redis-sentinel service may be vulnerable to integer overflow when parsing specially crafted large multi-bulk network replies. This is a result of a vulnerability in the underlying hiredis library which does not perform an overflow check before calling the calloc() heap allocation function. This issue only impacts systems with heap allocators that do not perform their own overflow checks. Most modern systems do and are therefore not likely to be affected. Furthermore, by default redis-sentinel uses the jemalloc allocator which is also not vulnerable. The problem is fixed in Redis versions 6.2.6, 6.0.16 and 5.0.14.
CWE description: The product performs a calculation to determine how much memory to allocate, but an integer overflow can occur that causes less memory to be allocated than expected, leading to a buffer overflow.
CVSS v3 base score: 8.8
Published: 2021-10-04T18:15Z
Repository: https://github.com/redis/redis
Language: C
Files changed: deps/hiredis/hiredis.c, deps/hiredis/test.c
Commit date: 2021-10-04 12:10:17 +0300
Commit message: Fix redis-cli / redis-sential overflow on some platforms (CVE-2021-32762) (#9587)

The redis-cli command line tool and redis-sentinel service may be vulnerable
to integer overflow when parsing specially crafted large multi-bulk network
replies. This is a result of a vulnerability in the underlying hiredis
library which does not perform an overflow check before calling the calloc()
heap allocation function.

This issue only impacts systems with heap allocators that do not perform their
own overflow checks. Most modern systems do and are therefore not likely to
be affected. Furthermore, by default redis-sentinel uses the jemalloc allocator
which is also not vulnerable.

Co-authored-by: Yossi Gottlieb <yossigo@gmail.com>
Diff: diff --git a/deps/hiredis/hiredis.c b/deps/hiredis/hiredis.c
index 51f22a665..990f61960 100644
--- a/deps/hiredis/hiredis.c
+++ b/deps/hiredis/hiredis.c
@@ -172,10 +172,11 @@ static void *createArrayObject(const redisReadTask *task, size_t elements) {
     r = createReplyObject(task->type);
     if (r == NULL)
         return NULL;
 
     if (elements > 0) {
+        if (SIZE_MAX / sizeof(redisReply*) < elements) return NULL;  /* Don't overflow */
         r->element = hi_calloc(elements,sizeof(redisReply*));
         if (r->element == NULL) {
             freeReplyObject(r);
             return NULL;
         }
diff --git a/deps/hiredis/test.c b/deps/hiredis/test.c
index 829536739..bdff74e88 100644
--- a/deps/hiredis/test.c
+++ b/deps/hiredis/test.c
@@ -496,10 +496,24 @@ static void test_reply_reader(void) {
     test_cond(ret == REDIS_ERR &&
               strcasecmp(reader->errstr, "Multi-bulk length out of range") == 0);
     freeReplyObject(reply);
     redisReaderFree(reader);
 
+    test("Multi-bulk never overflows regardless of maxelements: ");
+    size_t bad_mbulk_len = (SIZE_MAX / sizeof(void *)) + 3;
+    char bad_mbulk_reply[100];
+    snprintf(bad_mbulk_reply, sizeof(bad_mbulk_reply), "*%llu\r\n+asdf\r\n",
+        (unsigned long long) bad_mbulk_len);
+
+    reader = redisReaderCreate();
+    reader->maxelements = 0;    /* Don't rely on default limit */
+    redisReaderFeed(reader, bad_mbulk_reply, strlen(bad_mbulk_reply));
+    ret = redisReaderGetReply(reader,&reply);
+    test_cond(ret == REDIS_ERR && strcasecmp(reader->errstr, "Out of memory") == 0);
+    freeReplyObject(reply);
+    redisReaderFree(reader);
+
 #if LLONG_MAX > SIZE_MAX
     test("Set error when array > SIZE_MAX: ");
     reader = redisReaderCreate();
     redisReaderFeed(reader, "*9223372036854775807\r\n+asdf\r\n",29);
     ret = redisReaderGetReply(reader,&reply);

Fixed code:         if (SIZE_MAX / sizeof(redisReply*) < elements) return NULL;  /* Don't overflow */
    test("Multi-bulk never overflows regardless of maxelements: ");
    size_t bad_mbulk_len = (SIZE_MAX / sizeof(void *)) + 3;
    char bad_mbulk_reply[100];
    snprintf(bad_mbulk_reply, sizeof(bad_mbulk_reply), "*%llu\r\n+asdf\r\n",
        (unsigned long long) bad_mbulk_len);

    reader = redisReaderCreate();
    reader->maxelements = 0;    /* Don't rely on default limit */
    redisReaderFeed(reader, bad_mbulk_reply, strlen(bad_mbulk_reply));
    ret = redisReaderGetReply(reader,&reply);
    test_cond(ret == REDIS_ERR && strcasecmp(reader->errstr, "Out of memory") == 0);
    freeReplyObject(reply);
    redisReaderFree(reader);