Subvert Code-signing Facilities |
Attack Pattern ID: 68 (Standard Attack Pattern Completeness: Complete) | Typical Severity: Very High | Status: Draft |
Summary
Because languages use code signing facilities to vouch for code's identity and to thus tie code to its assigned privileges within an environment, subverting this mechanism can be instrumental in an attacker escalating privilege.
Any means of subverting the way that a virtual machine enforces code signing classifies for this style of attack. This pattern does not include circumstances through which a signing key has been stolen.
A framework-based language that supports code signing (such as, and most commonly, Java or .NET)
Deployed code that has been signed by its authoring vendor, or a partner.
The attacker will, for most circumstances, also need to be able to place code in the victim container. This does not necessarily mean that they will have to subvert host-level security, except when explicitly indicated.
Description
In old versions (prior to 3.0b4) of the Netscape web browser Attackers able to foist a malicious Applet into a client's browser could execute the "Magic Coat" attack. In this attack, the offending Applet would implement its own getSigners() method. This implementation would use the containing VM's APIs to acquire other Applet's signatures (by calling _their_ getSigners() method) and if any running Applet had privileged-enough signature, the malicious Applet would have inherited that privilege just be (metaphorically) donning the others' coats.
Description
Some (older) web browsers allowed scripting languages, such as Javascript, to call signed Java code. In these circumstances, the browser's VM implimentation would choose not to conduct stack inspection across language boundaries (from called signed Java to calling Javascript) and would short-circuit "true" at the language boundary. Doing so meant that the VM would allow any (unprivileged) script to call privileged funcitons within signed code with impunity, causing them to fall prey to luring attacks.
Description
The ability to load unsigned code into the kernel of earlier versions of Vista and bypass integrity checking is an example of such subversion. In the proof-of-concept, it is possible to bypass the signature-checking mechanism Vista uses to load device drivers.
Skill or Knowledge Level: High
Subverting code signing is not a trivial activity. Most code signing and verification schemes are based on use of cryptography and the attacker needs to have an understand of these cryptographic operations in good detail. Additionally the attacker also needs to be aware of the way memory is assigned and accessed by the container since, often, the only way to subvert code signing would be to patch the code in memory.
Finally, a knowledge of the platform specific mechanisms of signing and verifying code is a must.
The Attacker needs no special resources beyond the listed pre-requisities in order to conduct this style of attack.
Understanding, and possibly exploiting, the effect of certain flags or environment variables on code signing.
Introducing unmanaged code into a container-managed environment
A given code signing scheme may be fallible due to improper use of cryptography. Developers must never roll out their own cryptography, nor should existing primitives be modified or ignored.
If an attacker cannot attack the scheme directly, he might try to alter the environment that affects the signing and verification processes. A possible mitigation is to avoid reliance on flags or environment variables that are user-controllable.
Vulnerability ID | Relationship Description |
---|---|
CVE-2006-5201 | Multiple packages on Sun Solaris, including (1) NSS; (2) Java JDK and JRE 5.0 Update 8 and earlier, SDK and JRE 1.4.x up to 1.4.2_12, and SDK and JRE 1.3.x up to 1.3.1_19; (3) JSSE 1.0.3_03 and earlier; (4) IPSec/IKE; (5) Secure Global Desktop; and (6) StarOffice, when using an RSA key with exponent 3, removes PKCS-1 padding before generating a hash, which allows remote attackers to forge a PKCS #1 v1.5 signature that is signed by that RSA key and prevents these products from correctly verifying X.509 and other certificates that use PKCS #1. |
CVE-2006-4790 | verify.c in GnuTLS before 1.4.4, when using an RSA key with exponent 3, does not properly handle excess data in the digestAlgorithm.parameters field when generating a hash, which allows remote attackers to forge a PKCS #1 v1.5 signature that is signed by that RSA key and prevents GnuTLS from correctly verifying X.509 and other certificates that use PKCS, a variant of CVE-2006-4339. |
Nature | Type | ID | Name | Description | View(s) this relationship pertains to![]() |
---|---|---|---|---|---|
ChildOf | ![]() | 232 | Exploitation of Privilege/Trust | Mechanism of Attack (primary)1000 | |
ParentOf | ![]() | 206 | Lifting signing key and signing malicious code from a production environment | Mechanism of Attack (primary)1000 | |
ParentOf | ![]() | 237 | Calling signed code from another language within a sandbox that allows this | Mechanism of Attack (primary)1000 | |
ParentOf | ![]() | 238 | Using URL/codebase / G.A.C. (code source) to convince sandbox of privilege | Mechanism of Attack (primary)1000 |