From 21d7d94a16ed0be6e1fb101679bf9446b1163d44 Mon Sep 17 00:00:00 2001

From: Greg Hudson <ghudson@mit.edu>

Date: Mon, 17 Oct 2022 20:25:11 -0400

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.

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

the 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 950beda657..2e844d499b 100644

--- a/src/lib/krb5/krb/pac.c

+++ b/src/lib/krb5/krb/pac.c

@@ -29,6 +29,8 @@

 /* draft-brezak-win2k-krb-authz-00 */

+#define MAX_BUFFERS 4096

+

 /*

  * Add a buffer to the provided PAC and update header.

  */

@@ -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 ee47152ee4..ccd165380d 100644

--- a/src/lib/krb5/krb/t_pac.c

+++ b/src/lib/krb5/krb/t_pac.c

@@ -431,6 +431,16 @@ static const unsigned char s4u_pac_ent_xrealm[] = {

     0x8a, 0x81, 0x9c, 0x9c, 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 const char *s4u_principal = "w2k8u@ACME.COM";

 static const char *s4u_enterprise = "w2k8u@abc@ACME.COM";

@@ -646,6 +656,14 @@ main(int argc, char **argv)

         krb5_free_principal(context, sep);

     }

+    /* 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

      */

-- 

2.37.3