Public Vulnerability Reports

Multiple Unix/Linux Vendor cURL/libcURL Kerberos Authentication Buffer Overflow



cURL is a command line tool for transferring files with URL syntax,
supporting FTP, FTPS, HTTP, HTTPS, GOPHER, TELNET, DICT, FILE and LDAP. More information about cURL and libcURL is available from:


Remote exploitation of a stack-based buffer overflow in various Unix /
Linux vendors' implementation of cURL could allow for arbitrary code
execution on the targeted host.

An exploitable stack-based buffer overflow condition exists when using
Kerberos authentication. The problem specifically exists within the
functions Curl_krb_kauth() and krb4_auth() defined in lib/krb4.c.
Within these functions a statically allocated stack-based buffer of size
1250, from struct KTEXT_ST.dat, is passed to the Curl_base64_decode()
routine defined in lib/base64.c as can be seen here:

    len = Curl_base64_decode(p, (char *)adat.dat);
    tmp = Curl_base64_decode(p, (char *)tkt.dat);

The Curl_base64_decode() routine relies on the calling function to
validate the decoded length. This function base64 decodes and copies
data directly from the HTTP reply of a server to the destination buffer,
in this case buffer[]. An attacker can construct a long base64 encoded
malicious payload that upon decoding will overflow the static buffer and
overwrite the saved EIP. This in turn can lead to arbitrary code


Successful exploitation allows remote attackers to execute arbitrary code
under the privileges of the target user. Exploitation requires that an
attacker either coerce or force a target to connect to a malicious
server using Kerberos authentication.


iDEFENSE has confirmed the existence of this vulnerability in cURL
version 7.12.1. It is suspected that prior versions are affected as well.
Any application built using a vulnerable version libcURL will also be


Recompile cURL without Kerberos support if it is not needed.


No vendor response received.


 The Common Vulnerabilities and Exposures (CVE) project has assigned the
names CAN-2005-0490 to these issues. This is a candidate for inclusion
in the CVE list (, which standardizes names for
security problems.


12/23/2004   Initial vendor notification - No response
02/10/2005   Secondary vendor notification - No response
02/21/2005   Public disclosure


infamous41md[at] is credited with this discovery.

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Copyright © 2005 Verisign, Inc.

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