Linux Kernel SCTP-AUTH API Information Disclosure Vulnerability and NULL Pointer Dereferences

2008.09.18
Credit: Tobias Klein
Risk: Low
Local: Yes
Remote: No
CWE: CWE-200


CVSS Base Score: 4.7/10
Impact Subscore: 6.9/10
Exploitability Subscore: 3.4/10
Exploit range: Local
Attack complexity: Medium
Authentication: No required
Confidentiality impact: Complete
Integrity impact: None
Availability impact: None

Please find attached a detailed advisory of the vulnerabilities. Alternatively, the advisory can also be found at: http://www.trapkit.de/advisories/TKADV2008-007.txt -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Advisory: Linux Kernel SCTP-AUTH API Information Disclosure Vulnerability and NULL Pointer Dereferences Advisory ID: TKADV2008-007 Revision: 1.1 Release Date: 2008/09/09 Last Modified: 2008/09/10 Date Reported: 2008/08/20 Author: Tobias Klein (tk at trapkit.de) Affected Software: Linux Kernel <= 2.6.26.4 Remotely Exploitable: No Locally Exploitable: Yes Vendor URL: http://www.kernel.org/ Vendor Status: Vendor has released a fixed version CVE-ID: CVE-2008-3792 Patch development time: 1 day ====================== Vulnerability details: ====================== The Linux Kernel contains an information disclosure vulnerability while parsing the IOCTL SCTP_HMAC_IDENT. Exploitation of this vulnerability can allow a local unprivileged attacker to gain access to sensitive data. Additionally, there are various NULL pointer dereferences in the SCTP-AUTH API. All of the SCTP-AUTH socket options could cause a kernel panic if the extension is disabled and the API is envoked. Exploitation of these vulnerabilities can allow an unprivileged attacker to crash the system (Denial of Service). ====================== Technical description: ====================== - From source code file: net/sctp/socket.c [...] SCTP_STATIC int sctp_getsockopt(struct sock *sk, int level, int optname, char __user *optval, int __user *optlen) { int retval = 0; int len; [...] if (get_user(len, optlen)) <-- [1] return -EFAULT; [...] case SCTP_HMAC_IDENT: retval = sctp_getsockopt_hmac_ident(sk, len, optval, optlen); <-- [2] break; [...] [1] The user controlled value of "optlen" is copied into "len" [2] "len" is used as a parameter for the function "sctp_getsockopt_hmac_ident()" {...] static int sctp_getsockopt_hmac_ident(struct sock *sk, int len, char __user *optval, int __user *optlen) { struct sctp_hmac_algo_param *hmacs; __u16 param_len; hmacs = sctp_sk(sk)->ep->auth_hmacs_list; <-- [3] param_len = ntohs(hmacs->param_hdr.length); <-- [4] if (len < param_len) <-- [5] return -EINVAL; if (put_user(len, optlen)) return -EFAULT; if (copy_to_user(optval, hmacs->hmac_ids, len)) <-- [6] return -EFAULT; return 0; } [...] If SCTP authentication is disabled (net.sctp.auth_enable=0): [3] "hmacs" gets NULL [4] "hmacs->param_hdr.length" leads to a NULL pointer dereference That's one example of the mentioned NULL pointer dereferences in the SCTP-AUTH API. For more examples see [1]. If SCTP authentication is enabled (net.sctp.auth_enable=1): [3] "hmacs" gets a valid value [4] "param_len" gets a valid value [5] The length check can be easily passed as "len" is user controlled [6] "len" is a user controlled value, therefore it is possible to control the number of bytes that get copied back to the user As "len" isn't validated at all an unprivileged user can read arbitrary data from memory. ========= Solution: ========= The Linux Kernel maintainers have addressed these vulnerabilities within version 2.6.26.4. More information can be found from the URLs shown below. http://www.kernel.org/pub/linux/kernel/v2.6/ChangeLog-2.6.26.4 http://git.kernel.org/?p=linux/kernel/git/stable/linux- 2.6.26.y.git;a=commit;h=be9467bd75b522a3db0369c12db739f797cfec6a ======== History: ======== 2008/08/20 - Initial notification of kernel maintainers 2008/08/20 - Initial response from kernel maintainers 2008/09/08 - Fix provided 2008/09/09 - Public disclosure ======== Credits: ======== Vulnerabilities found and advisory written by Tobias Klein. =========== References: =========== [1] http://git.kernel.org/?p=linux/kernel/git/stable/linux-2.6.26.y.git ;a=commit;h=be9467bd75b522a3db0369c12db739f797cfec6a [2] http://www.kernel.org/pub/linux/kernel/v2.6/ChangeLog-2.6.26.4 [3] http://www.trapkit.de/advisories/TKADV2008-007.txt ======== Changes: ======== Revision 0.1 - Initial draft release to the vendor Revision 1.0 - Public release Revision 1.1 - Adjusted patch development time (thanks to Eugene Teo for pointing this out) and added CVE-ID. =========== Disclaimer: =========== The information within this advisory may change without notice. Use of this information constitutes acceptance for use in an AS IS condition. There are no warranties, implied or express, with regard to this information. In no event shall the author be liable for any direct or indirect damages whatsoever arising out of or in connection with the use or spread of this information. Any use of this information is at the user's own risk. ================== PGP Signature Key: ================== http://www.trapkit.de/advisories/tk-advisories-signature-key.asc Copyright 2008 Tobias Klein. All rights reserved. -----BEGIN PGP SIGNATURE----- wj8DBQFIyYqYkXxgcAIbhEERAuRXAJ4nWWaP5eHjDX+CG1TvoiPfR7CSoQCeLFtz Q+QTUjS3QmQmg7E+MiZN+3Y= =zxgA -----END PGP SIGNATURE-----

References:

http://www.trapkit.de/advisories/TKADV2008-007.txt
http://www.securityfocus.com/archive/1/archive/1/496256/100/0/threaded
http://www.kernel.org/pub/linux/kernel/v2.6/ChangeLog-2.6.26.4
http://git.kernel.org/?p=linux/kernel/git/stable/linux-2.6.26.y.git;a=commit;h=d97240552cd98c4b07322f30f66fd9c3ba4171de


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