CVE-2017-3224 in Quagga
Summary
by MITRE
Open Shortest Path First (OSPF) protocol implementations may improperly determine Link State Advertisement (LSA) recency for LSAs with MaxSequenceNumber. According to RFC 2328 section 13.1, for two instances of the same LSA, recency is determined by first comparing sequence numbers, then checksums, and finally MaxAge. In a case where the sequence numbers are the same, the LSA with the larger checksum is considered more recent, and will not be flushed from the Link State Database (LSDB). Since the RFC does not explicitly state that the values of links carried by a LSA must be the same when prematurely aging a self-originating LSA with MaxSequenceNumber, it is possible in vulnerable OSPF implementations for an attacker to craft a LSA with MaxSequenceNumber and invalid links that will result in a larger checksum and thus a 'newer' LSA that will not be flushed from the LSDB. Propagation of the crafted LSA can result in the erasure or alteration of the routing tables of routers within the routing domain, creating a denial of service condition or the re-routing of traffic on the network. CVE-2017-3224 has been reserved for Quagga and downstream implementations (SUSE, openSUSE, and Red Hat packages).
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Analysis
by VulDB Data Team • 12/28/2024
The vulnerability described in CVE-2017-3224 represents a critical flaw in OSPF protocol implementations that affects the proper handling of Link State Advertisements with maximum sequence numbers. This issue specifically targets the Link State Database management within OSPF routers, where the protocol's logic for determining LSA recency becomes compromised when processing LSAs with MaxSequenceNumber values. The flaw stems from an interpretation gap in RFC 2328 section 13.1 that governs how routers should compare LSAs to determine which ones are more recent and therefore should be retained in the database. When sequence numbers match, the protocol specification mandates that checksums be compared to establish recency, with the larger checksum indicating a newer advertisement that should not be flushed from the database. However, this mechanism creates an exploitable condition when combined with the improper handling of self-originating LSAs that are prematurely aged to maximum sequence numbers.
The technical exploitation of this vulnerability occurs when an attacker crafts a malicious LSA with a MaxSequenceNumber value and deliberately invalidates the link information contained within it. This manipulation results in a calculated checksum that exceeds that of legitimate LSAs, causing the vulnerable OSPF implementation to incorrectly classify the forged advertisement as more recent than valid routing information. The fundamental flaw lies in how the protocol handles the comparison logic for LSAs that have reached their maximum sequence number, particularly when the RFC does not explicitly require that link values remain consistent during the premature aging process. This creates a scenario where routers will not flush the malicious LSA from their Link State Databases, leading to persistent corruption of routing information throughout the OSPF domain.
The operational impact of CVE-2017-3224 extends beyond simple denial of service conditions to potentially enable sophisticated traffic redirection attacks that can compromise network integrity and availability. When the forged LSA propagates through the OSPF routing domain, it can cause routers to update their routing tables with incorrect information, leading to traffic being rerouted through unintended paths or completely blocked from reaching its destination. This vulnerability affects implementations in major Linux distributions including SUSE, openSUSE, and Red Hat packages, indicating a widespread exposure across enterprise and infrastructure networks that rely on OSPF for internal routing. The attack vector allows for persistent manipulation of routing tables, potentially enabling man-in-the-middle scenarios or complete network partitioning, making this a particularly dangerous vulnerability for network security.
Security mitigations for CVE-2017-3224 should focus on implementing proper sequence number validation and checksum verification mechanisms within OSPF implementations, ensuring that LSAs with maximum sequence numbers undergo additional validation checks before being accepted into the Link State Database. Network administrators should consider applying vendor-specific patches and updates that address the improper handling of MaxSequenceNumber LSAs, particularly those that enforce stricter validation of link information within aged LSAs. The vulnerability aligns with CWE-248, which addresses "Uncaught Exception" in software systems, as the improper handling of edge cases in LSA processing creates an exception condition that leads to unexpected behavior. From an ATT&CK framework perspective, this vulnerability maps to T1562.001, "Impairing Security Tools", and T1071.003, "Application Layer Protocol: DNS", as it can be used to impair network security by manipulating routing information. Organizations should also implement network monitoring to detect anomalous LSA propagation patterns and establish proper access controls to prevent unauthorized network participation that could enable such attacks.