File 0013-Fix-integer-overflows-in-PAC-parsing.patch of Package krb5.26727

Overview Repositories Revisions Requests Users Attributes Meta

File 0013-Fix-integer-overflows-in-PAC-parsing.patch of Package krb5.26727

From f18f3fe6d52e335447ea4f32752db64c966d2b44 Mon Sep 17 00:00:00 2001
From: Samuel Cabrero <scabrero@suse.de>
Date: Mon, 7 Nov 2022 15:29:41 +0100
Subject: [PATCH] Fix integer overflows in PAC parsing

In krb5_parse_pac(), check for buffer counts large enough to threaten
integer overflow in the header length and memory length calculations.
Avoid potential integer overflows when checking the length of each
buffer.  Credit to OSS-Fuzz for discovering one of the issues.

CVE-2022-42898:

In MIT krb5 releases 1.8 and later, an authenticated attacker may be
able to cause a KDC or kadmind process to crash by reading beyond the
bounds of allocated memory, creating a denial of service.  A
privileged attacker may similarly be able to cause a Kerberos or GSS
application service to crash.  On 32-bit platforms, an attacker can
also cause insufficient memory to be allocated for the result,
potentially leading to remote code execution in a KDC, kadmind, or GSS
or Kerberos application server process.  An attacker with the
privileges of a cross-realm KDC may be able to extract secrets from a
KDC process's memory by having them copied into the PAC of a new
ticket.

ticket: 9074 (new)
tags: pullup
target_version: 1.20-next
target_version: 1.19-next
---
 src/lib/krb5/krb/pac.c   |  9 +++++++--
 src/lib/krb5/krb/t_pac.c | 18 ++++++++++++++++++
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/src/lib/krb5/krb/pac.c b/src/lib/krb5/krb/pac.c
index c9b5de30a..ff32092d1 100644
--- a/src/lib/krb5/krb/pac.c
+++ b/src/lib/krb5/krb/pac.c
@@ -27,6 +27,8 @@
 #include "k5-int.h"
 #include "authdata.h"
 
+#define MAX_BUFFERS 4096
+
 /* draft-brezak-win2k-krb-authz-00 */
 
 /*
@@ -316,6 +318,9 @@ krb5_pac_parse(krb5_context context,
     if (version != 0)
         return EINVAL;
 
+    if (cbuffers < 1 || cbuffers > MAX_BUFFERS)
+        return ERANGE;
+
     header_len = PACTYPE_LENGTH + (cbuffers * PAC_INFO_BUFFER_LENGTH);
     if (len < header_len)
         return ERANGE;
@@ -348,8 +353,8 @@ krb5_pac_parse(krb5_context context,
             krb5_pac_free(context, pac);
             return EINVAL;
         }
-        if (buffer->Offset < header_len ||
-            buffer->Offset + buffer->cbBufferSize > len) {
+        if (buffer->Offset < header_len || buffer->Offset > len ||
+            buffer->cbBufferSize > len - buffer->Offset) {
             krb5_pac_free(context, pac);
             return ERANGE;
         }
diff --git a/src/lib/krb5/krb/t_pac.c b/src/lib/krb5/krb/t_pac.c
index 61fb51a98..f015e7d8a 100644
--- a/src/lib/krb5/krb/t_pac.c
+++ b/src/lib/krb5/krb/t_pac.c
@@ -81,6 +81,16 @@ static const unsigned char saved_pac[] = {
     0x83, 0xb3, 0x13, 0x3f, 0xfc, 0x5c, 0x41, 0xad, 0xe2, 0x64, 0x83, 0xe0, 0x00, 0x00, 0x00, 0x00
 };
 
+static const unsigned char fuzz1[] = {
+    0x00, 0x00, 0x00, 0x10, 0x00, 0x00, 0x00, 0x00,
+    0x06, 0xff, 0xff, 0xff, 0x00, 0x00, 0xf5
+};
+
+static const unsigned char fuzz2[] = {
+    0x00, 0x00, 0x00, 0x20, 0x00, 0x00, 0x00, 0x00,
+    0x20, 0x20
+};
+
 static unsigned int type_1_length = 472;
 
 static const krb5_keyblock kdc_keyblock = {
@@ -227,6 +237,14 @@ main(int argc, char **argv)
 
     krb5_pac_free(context, pac);
 
+    /* Check problematic PACs found by fuzzing. */
+    ret = krb5_pac_parse(context, fuzz1, sizeof(fuzz1), &pac);
+    if (!ret)
+        err(context, ret, "krb5_pac_parse should have failed");
+    ret = krb5_pac_parse(context, fuzz2, sizeof(fuzz2), &pac);
+    if (!ret)
+        err(context, ret, "krb5_pac_parse should have failed");
+
     /*
      * Test empty free
      */
-- 
2.38.0

Places

File 0013-Fix-integer-overflows-in-PAC-parsing.patch of Package krb5.26727

Places