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GHSA-c8w6-x74f-vmg3 CVE-2026-104434

zebrad vulnerable to full node denial of service via crafted Sapling receiver in z_listunifiedreceivers

High crates.io
Severity
7.1 / 10
High · CVSS 4.0
Exploit chance (EPSS)
0.31%
Chance of exploitation in the next 30 days. Higher than 23.50% of scored vulnerabilities.
Known exploited
No
Not in CISA's catalog
Weakness
CWE-20 Improper Input Validation
CWE-248 Uncaught Exception
CWE-617 Reachable Assertion
CWE-754 Improper Check for Unusual or Exceptional Conditions
Fix
Available
2 packages have a fixed version

Description

Am I affected

You are affected if:

  1. You run zebrad up to and including v4.4.1.
  2. Your zebrad.toml sets rpc.listen_addr to a TCP address (RPC server is enabled).
  3. An attacker can authenticate to the RPC endpoint. With the default enable_cookie_auth = true, this requires the attacker to read the .cookie file (typically local access). With enable_cookie_auth = false, any network client reaching the RPC port can trigger it.

Summary

The z_listunifiedreceivers RPC handler panics when processing a structurally valid Unified Address whose Sapling receiver carries 43 bytes that fail cryptographic validation (sapling_crypto::PaymentAddress::from_bytes returns None for non-subgroup Jubjub points). The handler calls .expect("using data already decoded as valid") on the fallible result. Because Zebra's release profile sets panic = "abort", the panic terminates the entire node process, not just the RPC task.

Details

zcash_address::unified::Encoding::decode validates only the structural envelope of a Unified Address (F4Jumble, bech32m, typecode ordering, 43-byte length for Sapling). It does not validate that the embedded pk_d is a valid Jubjub subgroup point or that the diversifier produces a valid g_d preimage.

At zebra-rpc/src/methods.rs:2893, the handler calls Address::try_from_sapling(network, data), which delegates to sapling_crypto::PaymentAddress::from_bytes. When from_bytes returns None (most random 32-byte strings fail the subgroup check), the .expect() fires and the process aborts.

The same crate already handles this correctly in try_from_unified at zebra-chain/src/primitives/address.rs:99-110, which returns Err when from_bytes fails. The vulnerable code path bypasses this validated route.

Patches

zebra-rpc 8.0.0 and zebrad 4.5.0.

Replace .expect() with .map_err(|e| ErrorObject::owned(...)) for proper error propagation, or route through the existing try_from_unified path which already handles this case correctly.

Workarounds

  • Disable the RPC server by removing rpc.listen_addr from zebrad.toml.
  • Ensure enable_cookie_auth = true (the default) and restrict filesystem access to the .cookie file.
  • Place a reverse proxy in front of the RPC port that rejects z_listunifiedreceivers calls with untrusted address parameters.

Impact

A single authenticated RPC request terminates the zebrad process. The attack is repeatable on restart (the same request triggers the same abort), allowing an attacker to keep the node down indefinitely until the request is filtered upstream. Operators using lightwalletd backends, Zaino indexers, or mining pool infrastructure that forward RPC calls to zebrad may be exposed if the forwarding path passes through z_listunifiedreceivers.

Credit

Reported by @robustfengbin via a private GitHub Security Advisory submission.

Affected versions

crates.io

PackageVulnerableFixed in
zebra-rpc
< 8.0.0
8.0.0
zebrad
< 4.5.0
4.5.0

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

zebra-rpc crates.io → 8.0.0

cargo
cargo update -p zebra-rpc --precise 8.0.0

zebrad crates.io → 4.5.0

cargo
cargo update -p zebrad --precise 4.5.0

Severity breakdown

CVSS 4.0 7.1

CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Attack vector
Network
Attack complexity
Low
Attack requirements
None
Privileges required
Low
User interaction
None
Confidentiality (vulnerable system)
None
Integrity (vulnerable system)
None
Availability (vulnerable system)
High
Confidentiality (subsequent systems)
None
Integrity (subsequent systems)
None
Availability (subsequent systems)
None
Exploit maturity
Not defined
Scope
X

CVSS 3.1 6.5

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

Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

Weakness

CWE-20: Improper Input Validation

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.

How to prevent it
  • Architecture and Design: Consider using language-theoretic security (LangSec) techniques that characterize inputs using a formal language and build "recognizers" for that language. This effectively requires parsing to be a distinct layer that effectively enforces a boundary between raw input and internal data representations, instead of allowing parser code to be scattered throughout the program, where it could be subject to errors or inconsistencies that create weaknesses. [REF-1109] [REF-1110] [REF-1111]
  • Architecture and Design: Use an input validation framework such as Struts or the OWASP ESAPI Validation API. Note that using a framework does not automatically address all input validation problems; be mindful of weaknesses that could arise from misusing the framework itself (CWE-1173).
  • Architecture and Design, Implementation: Understand all the potential areas where untrusted inputs can enter the product, including but not limited to: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any external systems that provide data to the application. Remember that such inputs may be obtained indirectly through API calls.
  • Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
  • Architecture and Design: For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server. Even though client-side checks provide minimal benefits with respect to server-side security, they are still useful. First, they can support intrusion detection. If the server receives input that should have been rejected by the client, then it may be an indication of an attack. Second, client-side error-checking can provide helpful feedback to the user about the expectations for valid input. Third, there may be a reduction in server-side processing time for accidental input errors, although this is typically a small savings.
  • Implementation: When your application combines data from multiple sources, perform the validation after the sources have been combined. The individual data elements may pass the validation step but violate the intended restrictions after they have been combined.
  • Implementation: Be especially careful to validate all input when invoking code that crosses language boundaries, such as from an interpreted language to native code. This could create an unexpected interaction between the language boundaries. Ensure that you are not violating any of the expectations of the language with which you are interfacing. For example, even though Java may not be susceptible to buffer overflows, providing a large argument in a call to native code might trigger an overflow.
  • Implementation: Directly convert your input type into the expected data type, such as using a conversion function that translates a string into a number. After converting to the expected data type, ensure that the input's values fall within the expected range of allowable values and that multi-field consistencies are maintained.
  • Implementation: Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180, CWE-181). Make sure that your application does not inadvertently decode the same input twice (CWE-174). Such errors could be used to bypass allowlist schemes by introducing dangerous inputs after they have been checked. Use libraries such as the OWASP ESAPI Canonicalization control. Consider performing repeated canonicalization until your input does not change any more. This will avoid double-decoding and similar scenarios, but it might inadvertently modify inputs that are allowed to contain properly-encoded dangerous content.
  • Implementation: When exchanging data between components, ensure that both components are using the same character encoding. Ensure that the proper encoding is applied at each interface. Explicitly set the encoding you are using whenever the protocol allows you to do so.

CWE-248: Uncaught Exception

An exception is thrown from a function, but it is not caught.

CWE-617: Reachable Assertion

The product contains an assert() or similar statement that can be triggered by an attacker, which leads to an application exit or other behavior that is more severe than necessary.

How to prevent it
  • Implementation: Make sensitive open/close operation non reachable by directly user-controlled data (e.g. open/close resources)
  • Implementation: Perform input validation on user data.

CWE-754: Improper Check for Unusual or Exceptional Conditions

The product does not check or incorrectly checks for unusual or exceptional conditions that are not expected to occur frequently during day to day operation of the product.

How to prevent it
  • Requirements: Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. Choose languages with features such as exception handling that force the programmer to anticipate unusual conditions that may generate exceptions. Custom exceptions may need to be developed to handle unusual business-logic conditions. Be careful not to pass sensitive exceptions back to the user (CWE-209, CWE-248).
  • Implementation: Check the results of all functions that return a value and verify that the value is expected.
  • Implementation: If using exception handling, catch and throw specific exceptions instead of overly-general exceptions (CWE-396, CWE-397). Catch and handle exceptions as locally as possible so that exceptions do not propagate too far up the call stack (CWE-705). Avoid unchecked or uncaught exceptions where feasible (CWE-248).
  • Implementation: Ensure that error messages only contain minimal details that are useful to the intended audience and no one else. The messages need to strike the balance between being too cryptic (which can confuse users) or being too detailed (which may reveal more than intended). The messages should not reveal the methods that were used to determine the error. Attackers can use detailed information to refine or optimize their original attack, thereby increasing their chances of success. If errors must be captured in some detail, record them in log messages, but consider what could occur if the log messages can be viewed by attackers. Highly sensitive information such as passwords should never be saved to log files. Avoid inconsistent messaging that might accidentally tip off an attacker about internal state, such as whether a user account exists or not. Exposing additional information to a potential attacker in the context of an exceptional condition can help the attacker determine what attack vectors are most likely to succeed beyond DoS.
  • Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
  • Architecture and Design, Implementation: If the program must fail, ensure that it fails gracefully (fails closed). There may be a temptation to simply let the program fail poorly in cases such as low memory conditions, but an attacker may be able to assert control before the software has fully exited. Alternately, an uncontrolled failure could cause cascading problems with other downstream components; for example, the program could send a signal to a downstream process so the process immediately knows that a problem has occurred and has a better chance of recovery.
  • Architecture and Design: Use system limits, which should help to prevent resource exhaustion. However, the product should still handle low resource conditions since they may still occur.

References

Packages

Other links

Timeline

  1. Published
  2. Last updated by the source
  3. Latest EPSS score
AdvisorySeverityWhy it's related
GHSA-ww9q-8r59-xv46
Zebra: Missing copy constraint in halo2_gadgets variable-base scalar multiplication allows under-constrained base, breaking Orchard Action circuit soundness
Critical Also affects zebrad
GHSA-63wg-wjjj-7cp8
Zebra Address Book Aborted by IPv4-Mapped Mempool Misbehavior Update
High Also affects zebrad
GHSA-65jj-fmw8-468q
zebrad has unbounded memory leak in mempool download pipeline via timeout path cancel_handles retention
Medium Also affects zebrad
GHSA-2gf8-q9rr-jq3h
zebrad has persistent on-disk corruption of Sapling/Orchard subtree roots after chain fork via pop_tip
Medium Also affects zebrad
GHSA-hhm7-qrv5-h4r6
Zebra: Repeated Non-Finalized Shielded Transaction Aborts Zebra Before Duplicate-Nullifier Rejection
Medium Also affects zebrad
GHSA-w834-cf6p-9m9w
Zebra: Finalized address balance credit-first overflow on consensus-valid blocks
Medium Also affects zebrad
GHSA-gvjc-3w7c-92jx
Zebra has sync restart poisoning from single unauthenticated peer via above-lookahead block
Medium Also affects zebrad
GHSA-gf9r-m956-97qx
zebrad has consensus divergence via P2SH sigop undercount in pure-Rust disabled-opcode parser
Critical Also affects zebrad
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