CVE-2026-40881: Zebra: addr/addrv2 Deserialization Resource Exhaustion
CVE-2026-40881: addr/addrv2 Deserialization Resource Exhaustion
Summary
When deserializing addr or addrv2 messages, which contain vectors of addresses, Zebra would fully deserialize them up to a maximum length (over 233,000) that was derived from the 2 MiB message size limit. This is much larger than the actual limit of 1,000 messages from the specification. Zebra would eventually check that limit but, at that point, the memory for the larger vector was already allocated. An attacker could cause out-of-memory aborts in Zebra by sending multiple such messages over different connections.
Severity
Moderate - This is a Denial of Service Vulnerability that could allow an attacker to crash a Zebra node.
Affected Versions
All Zebra versions prior to version 4.3.1.
Description
The vulnerability exists in the readaddr/addrv2 functions in codec.rs. It deserializes a vector of addresses with the zcashdeserialize() trait method, which uses as a upper bound the result of T::maxallocation(). For theses types, it was derived from dividing the max message size (2 MiB) by the minimum serialized size of one entry. For AddrV1: 2097152 / 30 = 69,904. For AddrV2: 2097152 / 9 = 233,016. Only after deserialization was the MAXADDRSINMESSAGE = 1000 limit checked.
An attacker could exploit this by: 1. Creating addr or addrv2 messages with a large number of entries. 2. Submitting them to a Zebra node, possibly through multiple connections, to attempt to get Zebra into an out-of-memory state.
Impact
Denial of Service
Attack Vector: Network. Effect: Zebra node crash. Scope: Any impacted Zebra node.
Fixed Versions
This issue is fixed in Zebra 4.3.1.
The fix changes the maxallocation() method for the relevant types to return 1,000, thus blocking larger values prior to deserialization.
Mitigation
Users should upgrade to Zebra 4.3.1 or later immediately.
There are no known workarounds for this issue. Immediate upgrade is the only way to ensure the node remains not vulnerable to the denial of service attack.
Credits
Thanks @Zk-nd3r for finding and reporting the issue, and suggesting the fix.
Other sources
ZEBRA is a Zcash node written entirely in Rust. Prior to zebrad version 4.3.0 and zebra-network version 5.0.1, when deserializing addr or addrv2 messages, which contain vectors of addresses, Zebra would fully deserialize them up to a maximum length (over 233,000) that was derived from the 2 MiB message size limit. This is much larger than the actual limit of 1,000 messages from the specification. Zebra would eventually check that limit but, at that point, the memory for the larger vector was already allocated. An attacker could cause out-of-memory aborts in Zebra by sending multiple such messages over different connections. This vulnerability is fixed in zebrad version 4.3.0 and zebra-network version 5.0.1.
— MITRE
Affected Software
Event History
Frequently Asked Questions
What is the severity of CVE-2026-40881?
CVE-2026-40881 is classified as a resource exhaustion vulnerability, which can lead to denial-of-service conditions.
How do I fix CVE-2026-40881?
To mitigate CVE-2026-40881, upgrade to zebra-network version 5.0.1 or zebrad version 4.3.1 or later.
What systems are affected by CVE-2026-40881?
CVE-2026-40881 affects systems using zebra-network versions prior to 5.0.1 and zebrad versions prior to 4.3.1.
What type of attack does CVE-2026-40881 enable?
CVE-2026-40881 enables attackers to exploit resource exhaustion issues through excessive address vector deserialization.
Is CVE-2026-40881 easily exploitable?
CVE-2026-40881 may be exploited through targeted attacks involving large deserialization inputs.