CVE-2020-13111 (published 2020-05-16T15:15Z)

NaviServer 4.99.4 to 4.99.19 allows denial of service due to the nsd/driver.c ChunkedDecode function not properly validating the length of a chunk. A remote attacker can craft a chunked-transfer request that will result in a negative value being passed to memmove via the size parameter, causing the process to crash.

Severity: MEDIUM
CVSS v2 base score: 5.0 (AV:N/AC:L/Au:N/C:N/I:N/A:P)
CVSS v3 base score: 7.5, HIGH (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

Weakness information:
cwe_id: CWE-20
cwe_name: Improper Input Validation
description: The product receives input or data, but it does
        not validate or incorrectly validates that the input has the
        properties that are required to process the data safely and
        correctly.
extended_description: 
	   Input validation is a frequently-used technique
	   for checking potentially dangerous inputs in order to
	   ensure that the inputs are safe for processing within the
	   code, or when communicating with other components.  When
	   software does not validate input properly, an attacker is
	   able to craft the input in a form that is not expected by
	   the rest of the application. This will lead to parts of the
	   system receiving unintended input, which may result in
	   altered control flow, arbitrary control of a resource, or
	   arbitrary code execution.
	   Input validation is not the only technique for
	   processing input, however.  Other techniques attempt to
	   transform potentially-dangerous input into something safe, such
	   as filtering (CWE-790) - which attempts to remove dangerous
	   inputs - or encoding/escaping (CWE-116), which attempts to
	   ensure that the input is not misinterpreted when it is included
	   in output to another component. Other techniques exist as well
	   (see CWE-138 for more examples.)
	   Input validation can be applied to:
	   
	     raw data - strings, numbers, parameters, file contents, etc.
	     metadata - information about the raw data, such as headers or size
	   
	   Data can be simple or structured.  Structured data
	   can be composed of many nested layers, composed of
	   combinations of metadata and raw data, with other simple or
	   structured data.
	   Many properties of raw data or metadata may need
	   to be validated upon entry into the code, such
	   as:
	   
	     specified quantities such as size, length, frequency, price, rate, number of operations, time, etc.
	     implied or derived quantities, such as the actual size of a file instead of a specified size
	     indexes, offsets, or positions into more complex data structures
	     symbolic keys or other elements into hash tables, associative arrays, etc.
	     well-formedness, i.e. syntactic correctness - compliance with expected syntax 
	     lexical token correctness - compliance with rules for what is treated as a token
	     specified or derived type - the actual type of the input (or what the input appears to be)
	     consistency - between individual data elements, between raw data and metadata, between references, etc.
	     conformance to domain-specific rules, e.g. business logic 
	     equivalence - ensuring that equivalent inputs are treated the same
	     authenticity, ownership, or other attestations about the input, e.g. a cryptographic signature to prove the source of the data
	   
	   Implied or derived properties of data must often
	   be calculated or inferred by the code itself.  Errors in
	   deriving properties may be considered a contributing factor
	   to improper input validation.
	   
	   Note that "input validation" has very different
	   meanings to different people, or within different
	   classification schemes.  Caution must be used when
	   referencing this CWE entry or mapping to it.  For example,
	   some weaknesses might involve inadvertently giving control
	   to an attacker over an input when they should not be able
	   to provide an input at all, but sometimes this is referred
	   to as input validation.
	   Finally, it is important to emphasize that the
	   distinctions between input validation and output escaping
	   are often blurred, and developers must be careful to
	   understand the difference, including how input validation
	   is not always sufficient to prevent vulnerabilities,
	   especially when less stringent data types must be
	   supported, such as free-form text. Consider a SQL injection
	   scenario in which a person's last name is inserted into a
	   query. The name "O'Reilly" would likely pass the validation
	   step since it is a common last name in the English
	   language. However, this valid name cannot be directly
	   inserted into the database because it contains the "'"
	   apostrophe character, which would need to be escaped or
	   otherwise transformed. In this case, removing the
	   apostrophe might reduce the risk of SQL injection, but it
	   would produce incorrect behavior because the wrong name
	   would be recorded.
       
         
cwe_id: CWE-787
cwe_name: Out-of-bounds Write
description: The product writes data past the end, or before the beginning, of the intended buffer.
extended_description: 
            
            
             
			 
         
         

Fix information:
repo_url: https://bitbucket.org/naviserver/naviserver
commit_details: repo_url: https://bitbucket.org/naviserver/naviserver
author: Gustaf Neumann
author_date: 2020-05-16 13:34:36+02:00
msg: fix for bug https://sourceforge.net/p/naviserver/bugs/89/

A negative value provided as chunk encoding length led to a potential crash.
A test case for this case was added to the regression test.
repository: repo_url: https://bitbucket.org/naviserver/naviserver
repo_name: visit repo url
description: visit repo url
repo_language: visit repo url
owner: naviserver
file_changes: filename: driver.c
change_type: ModificationType.MODIFY
diff: @@ -287,7 +287,7 @@ static NS_POLL_NFDS_TYPE PollSet(PollData *pdata, NS_SOCKET sock, short type, co
     NS_GNUC_NONNULL(1);
 static int PollWait(const PollData *pdata, int timeout)
     NS_GNUC_NONNULL(1);
-static bool ChunkedDecode(Request *reqPtr, bool update)
+static SockState ChunkedDecode(Request *reqPtr, bool update)
     NS_GNUC_NONNULL(1);
 static WriterSock *WriterSockRequire(const Conn *connPtr)
     NS_GNUC_NONNULL(1);
@@ -3374,20 +3374,22 @@ SockClose(Sock *sockPtr, int keep)
  *      shorter than the encoded one.
  *
  * Results:
- *      NS_TRUE when chunk was complete, NS_FALSE otherwise
+ *      SOCK_READY when chunk was complete, SOCK_MORE when more data is
+ *      requried, or some error condition.
  *
  * Side effects:
- *      updates the buffer if update is true (and adjusts reqPtr->chunkWriteOff)
- *      updates always reqPtr->chunkStartOff to allow incremental operations
+ *      Updates the buffer if update is true (and adjusts
+ *      reqPtr->chunkWriteOff).  Updates always reqPtr->chunkStartOff to allow
+ *      incremental operations.
  *
  *----------------------------------------------------------------------
  */
-static bool
+static SockState
 ChunkedDecode(Request *reqPtr, bool update)
 {
     const Tcl_DString *bufPtr;
     const char        *end, *chunkStart;
-    bool              success = NS_TRUE;
+    SockState         result = SOCK_READY;
 
     NS_NONNULL_ASSERT(reqPtr != NULL);
 
@@ -3397,35 +3399,41 @@ ChunkedDecode(Request *reqPtr, bool update)
 
     while (reqPtr->chunkStartOff <  (size_t)bufPtr->length) {
         char   *p = strstr(chunkStart, "\r\n");
-        size_t  chunk_length;
+        long    chunkLength;
 
         if (p == NULL) {
             Ns_Log(DriverDebug, "ChunkedDecode: chunk did not find end-of-line");
-            success = NS_FALSE;
+            result = SOCK_MORE;
             break;
         }
 
         *p = '\0';
-        chunk_length = (size_t)strtol(chunkStart, NULL, 16);
+        chunkLength = strtol(chunkStart, NULL, 16);
+        *p = '\r';
+        if (chunkLength < 0) {
+            Ns_Log(Warning, "ChunkedDecode: negative chunk length");
+            result = SOCK_BADREQUEST;
+            break;
+        }
         *p = '\r';
 
-        if (p + 2 + chunk_length > end) {
+        if (p + 2 + chunkLength > end) {
             Ns_Log(DriverDebug, "ChunkedDecode: chunk length past end of buffer");
-            success = NS_FALSE;
+            result = SOCK_MORE;
             break;
         }
         if (update) {
             char *writeBuffer = bufPtr->string + reqPtr->chunkWriteOff;
 
-            memmove(writeBuffer, p + 2, chunk_length);
-            reqPtr->chunkWriteOff += chunk_length;
-            *(writeBuffer + chunk_length) = '\0';
+            memmove(writeBuffer, p + 2, (size_t)chunkLength);
+            reqPtr->chunkWriteOff += (size_t)chunkLength;
+            *(writeBuffer + chunkLength) = '\0';
         }
-        reqPtr->chunkStartOff += (size_t)(p - chunkStart) + 4u + chunk_length;
+        reqPtr->chunkStartOff += (size_t)(p - chunkStart) + 4u + (size_t)chunkLength;
         chunkStart = bufPtr->string + reqPtr->chunkStartOff;
     }
 
-    return success;
+    return result;
 }
 
 
@@ -4114,7 +4122,7 @@ SockParse(Sock *sockPtr)
     /*
      * Check if all content has arrived.
      */
-    Ns_Log(Dev, "=== length < avail (length %" PRIuz
+    Ns_Log(Debug, "=== length < avail (length %" PRIuz
            ", avail %" PRIuz ") tfd %d tfile %p chunkStartOff %" PRIuz,
            reqPtr->length, reqPtr->avail, sockPtr->tfd,
            (void *)sockPtr->tfile, reqPtr->chunkStartOff);
@@ -4123,10 +4131,10 @@ SockParse(Sock *sockPtr)
         /*
          * Chunked encoding was provided.
          */
-        bool   complete;
-        size_t currentContentLength;
+        SockState chunkState;
+        size_t    currentContentLength;
 
-        complete = ChunkedDecode(reqPtr, NS_TRUE);
+        chunkState = ChunkedDecode(reqPtr, NS_TRUE);
         currentContentLength = reqPtr->chunkWriteOff - reqPtr->coff;
 
         /*
@@ -4136,12 +4144,15 @@ SockParse(Sock *sockPtr)
          * "expectedLength" was provided by the client, we terminate
          * depending on that information
          */
-        if ((!complete)
+        if ((chunkState == SOCK_MORE)
             || (reqPtr->expectedLength != 0u && currentContentLength < reqPtr->expectedLength)) {
             /*
              * ChunkedDecode wants more data.
              */
             return SOCK_MORE;
+
+        } else if (chunkState != SOCK_READY) {
+            return chunkState;
         }
         /*
          * ChunkedDecode has enough data.

programming_language: C
filename: http_chunked.test
change_type: ModificationType.MODIFY
diff: @@ -130,8 +130,27 @@ test http_chunked-2.3 {
     ns_unregister_op GET /tclchunked
 } -result {200 {} 5 01234}
 
+test http_chunked-2.4 {
 
-test http_chunked-3-1 {
+    POST request with invalid chunked content
+
+} -constraints serverListen -setup {
+    ns_register_proc PUT /tclchunked {
+        set content [ns_conn content]
+        #ns_log notice "PUT received <$content>"
+        ns_return 200 text/plain $content
+    }
+} -body {
+    nstest::http-0.9 -http 1.1 \
+        -omitcontentlength 1 \
+        -setheaders {Transfer-Encoding Chunked} \
+        -getheaders {Transfer-Encoding Content-Length} -getbody 1 \
+        PUT /tclchunked "-1\r\nchunk\r\n0\r\n\r\n"
+} -cleanup {
+    ns_unregister_op PUT /tclchunked
+} -match glob -result {200 {} 0 {HTTP/1.0 400 Bad Request*}}
+
+test http_chunked-3.1 {
 
     PUT with Transfer-Encoding Chunked and unknown Content-Length (but
     provided X-Expected-Entity-Length). This is the format that WebDAV

programming_language: Shell