VulnerabilityPublished 2 Jul 2026

Zebra network: Zebra has pre-handshake buffer capacity reservation based on attacker-claimed body length

Affects zebra-networkSource GCVE Database

CVSS 3.7 Low : upgrade to 7.0.0 when convenient.

Data as of 3 Jul 2026, 22:49 UTC

CVSS 3.1 base score

3.7Low

How severe the flaw is on the 0–10 CVSS scale.

Patch: Available – fixed in 7.0.0, 4.5.0

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L

Attack Vector: Network
Attack Complexity: High
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: Low

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: High: A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

Definitions: FIRST CVSS v3.1 specification.

What to do

Upgrade zebra-network to 7.0.0; zebrad to 4.5.0.

Affected software

Product	Affected	Fixed in
crates.iozebra-network	Affected <7.0.0	Fixed in 7.0.0
crates.iozebrad	Affected <4.5.0	Fixed in 4.5.0

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AI-suggested

A fix is available that defers large buffer reservations until after handshake completion or caps the reservation size for pre-handshake messages. No workaround is necessary as existing per-IP connection limits, handshake timeouts, and accept rate limits effectively mitigate the practical impact. Users should apply the official fix when available to improve defense-in-depth.

Description

### Am I affected You are affected if: 1. You run `zebrad` up to and including `v4.4.1`. 2. Your node accepts inbound P2P connections (`network.listen_addr` is set, which is the default). ### Summary The P2P codec's `Codec::decode()` method calls `src.reserve(body_len + HEADER_LEN)` after parsing a 24-byte protocol header, using the attacker-claimed `body_len` field. This reserves up to `MAX_PROTOCOL_MESSAGE_LEN` (~2 MiB) of virtual buffer capacity per connection before any body bytes arrive and before the handshake completes. However, `BytesMut::reserve()` sets virtual capacity without committing physical memory pages. The operating system does not allocate physical RAM until bytes are actually written into the buffer. Since the attacker never sends body bytes, the reserved capacity remains uncommitted. Reproduction of the reporter's PoC (256 threads, 30 seconds of sustained connections) showed negligible RSS impact on the Zebra process. Zebra's existing mitigations further constrain the practical attack surface: per-IP connection limits (`max_connections_per_ip = 1`), a per-connection accept rate of approximately one per second, and a 3-second handshake timeout that cleans up idle connections. ### Details At `zebra-network/src/protocol/external/codec.rs:406`, after parsing the 24-byte header and validating the network magic and body length against `MAX_PROTOCOL_MESSAGE_LEN`, the codec calls `src.reserve(body_len + HEADER_LEN)`. The codec is constructed on the bare TCP stream before `negotiate_version()` runs, so the reservation is reachable from any TCP peer that can send 24 bytes. No legitimate Zcash handshake message (`version`, `verack`) is anywhere close to 2 MiB. The codec makes no distinction between pre-handshake and post-handshake message types when sizing the reservation. ### Patches The fix defers large buffer reservations until after the handshake completes, or caps the per-message reservation for pre-handshake messages to what `version`/`verack` actually require. ### Workarounds No workaround is needed. The existing per-IP rate limiting, handshake timeout, and connection limits effectively mitigate the practical impact. ### Impact Minimal. The reservation affects virtual address space only, not physical memory. Zebra's existing connection-management mitigations (per-IP limits, accept rate, handshake timeout) further constrain the attack. The code path is worth cleaning up for defense-in-depth but does not produce a measurable denial-of-service effect. ### Credit Reported by `@ouicate` via a private GitHub Security Advisory submission.

Impact

The vulnerability only affects virtual address space reservation without allocating physical memory, resulting in minimal impact. Existing mitigations such as limiting connections per IP, handshake timeouts, and connection accept rates effectively prevent practical denial-of-service. There is no measurable increase in resource usage or service disruption demonstrated by the reporter's proof of concept.

CWE-770Allocation of Resources Without Limits or Throttling (opens in a new tab)
Base weaknessLikelihood of exploit: HighCWE Top 25 (2025): #25
The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.
Requirements
Clearly specify the minimum and maximum expectations for capabilities, and dictate which behaviors are acceptable when resource allocation reaches limits.
Architecture and Design
Limit the amount of resources that are accessible to unprivileged users. Set per-user limits for resources. Allow the system administrator to define these limits. Be careful to avoid CWE-410.
Architecture and Design
Design throttling mechanisms into the system architecture. The best protection is to limit the amount of resources that an unauthorized user can cause to be expended.
OWASP Cheat Sheets
Abuse Case (opens in a new tab)
OWASP ASVS 4.0.3
V8.1.4 (opens in a new tab)
V13.4.1 (opens in a new tab)
V11.1.4 (opens in a new tab)
Attack patterns
XML Ping of the Death (opens in a new tab)
Exponential Data Expansion (opens in a new tab)
Serialized Data Parameter Blowup (opens in a new tab)
Serialized Data with Nested Payloads (opens in a new tab)
Oversized Serialized Data Payloads (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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What to do

Affected software

Description

AI analysisMachine-generated, updated 2 Jul 2026, 23:11 UTC

WeaknessesCWE-770

Technical details

References

Community reviews

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