CVE-2012-4419 in Tor
Summary
by MITRE
The compare_tor_addr_to_addr_policy function in or/policies.c in Tor before 0.2.2.39, and 0.2.3.x before 0.2.3.21-rc, allows remote attackers to cause a denial of service (assertion failure and daemon exit) via a zero-valued port field that is not properly handled during policy comparison.
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Analysis
by VulDB Data Team • 04/13/2021
The vulnerability identified as CVE-2012-4419 represents a critical denial of service flaw within the Tor anonymization network software. This issue affects versions of Tor prior to 0.2.2.39 and 0.2.3.21-rc, specifically targeting the compare_tor_addr_to_addr_policy function located in the or/policies.c source file. The flaw stems from inadequate handling of zero-valued port fields during policy comparison operations, creating a scenario where malicious actors can exploit this weakness to disrupt Tor daemon operations.
The technical implementation of this vulnerability involves the compare_tor_addr_to_addr_policy function which is responsible for validating and comparing network addresses against policy configurations. When a zero-valued port field is encountered during policy evaluation, the function fails to properly validate this input condition, leading to an assertion failure that ultimately causes the Tor daemon to terminate unexpectedly. This assertion failure represents a fundamental breakdown in input validation and error handling mechanisms within the Tor codebase, as the system does not adequately account for edge cases involving null or zero port values.
From an operational perspective, this vulnerability presents significant risks to the Tor network's stability and availability. Remote attackers can exploit this weakness by crafting malicious network requests containing zero-valued port fields, which when processed by vulnerable Tor instances trigger immediate daemon termination. This creates a denial of service condition that can be systematically exploited to disrupt Tor relay operations, potentially compromising the anonymity services that depend on these network nodes. The impact extends beyond individual node failures as it can affect the overall network topology and routing capabilities of the Tor infrastructure.
The vulnerability aligns with CWE-682, which classifies improper arithmetic operations, specifically addressing cases where software performs operations on values that are not properly validated or handled. Additionally, this flaw relates to ATT&CK technique T1499.004, which covers network disruption through denial of service attacks targeting network infrastructure components. The issue demonstrates poor input validation practices that could be exploited in broader attack scenarios where adversaries seek to destabilize network services or compromise the availability of anonymity networks.
Mitigation strategies for this vulnerability involve updating to patched versions of Tor software where the compare_tor_addr_to_addr_policy function has been corrected to properly handle zero-valued port fields. System administrators should immediately deploy the updated versions 0.2.2.39 and 0.2.3.21-rc or later, as these releases contain the necessary fixes to prevent assertion failures during policy comparison operations. Network monitoring should also be enhanced to detect unusual daemon termination patterns that might indicate exploitation attempts, while implementing proper input validation at multiple layers of the network stack to prevent similar issues in other components.