From 06d30f43a41029d83248bbac1a9b65fc09987597 Mon Sep 17 00:00:00 2001 From: Greg Hudson 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..1b9ef12276 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 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