CVE-2026-24889: Silent Arithmetic Overflow in soroban-sdk Puts Smart Contract Integrity at Risk

Aegiron 13 mins0

CVE-2026-24889 — soroban-sdk Arithmetic Overflow / Range Handling Bug

CVE: CVE-2026-24889
Product: rs-soroban-sdk (Rust SDK for Soroban smart contracts)
CVSS v3.1 Score: 5.3 (Medium)
Severity: Moderate ­– affects contract logic integrity in specific builds
Exploitability: Limited but realistic when specific conditions are met
Exploit Availability: No public proof-of-concept (PoC) widely published

Official patch / upgrade links: Links provided below

Overview

CVE-2026-24889 is a flaw in the rs-soroban-sdk library where certain numeric operations produce silent overflow/wraparound when contracts are compiled without overflow checks enabled. In Rust, arithmetic operations can either trap on overflow or wrap around silently depending on compiler settings. The affected functions (Bytes::slice, Vec::slice, Prng::gen_range) used unchecked arithmetic when adjusting bounds, so if an attacker or contract logic passed values at the numeric limits, the resulting values could wrap instead of erroring.

As a result, the range values sent to the Soroban host could be completely different from what the developer intended, leading to downstream effects such as reading incorrect data, generating random values from the wrong domain, or working with slices that are empty or far too large.

This issue is subtle because it does not always trigger an explicit crash or error. Instead, it quietly changes how the contract behaves, which is more insidious and harder to detect in general testing unless you focus on boundary inputs.

How It Can Be Exploited

This vulnerability requires specific conditions:

  1. The contract must use functions like Bytes::slice, Vec::slice, or Prng::gen_range::<u64>.
  2. The contract must be compiled without overflow checks enabled (the Rust default for release builds unless overridden).
  3. The attacker must provide or influence values that are near the numeric limits (e.g., maximum possible unsigned integer values or zero bounds).

Attack Scenario (Simplified)

Imagine a smart contract that slices a user-provided byte array from index start to index end. If the contract logic does not validate that end is within safe limits, and the caller sends the maximum possible value, the code might do something like:

  • Add 1 to end to convert an inclusive range into an exclusive end bound.
  • In unchecked arithmetic, this wraps around to zero instead of failing.
  • The resulting slice range becomes empty or invalid instead of being what was expected.

Similarly, a “random range” generation function might subtract from zero or add to the maximum value, leading to a full-range output when the intention was to generate within a specific limited range.

An attacker can trigger this quietly by providing crafted inputs to the contract if the contract does not do its own bound checks.

Practical Impact

  • This is not remotely exploitable in all contracts — only those that forward unvalidated numeric inputs into the range-handling functions without overflow checks.
  • The impact is contract logic corruption, not direct remote code execution or blockchain consensus compromise.
  • Effects can include:
    • Reading incorrect segments of data
    • Producing empty or unexpected slices
    • Generating random numbers outside intended ranges
    • Breaking audit expectations and business logic invariants

The issue does not reveal secrets, crash the host, or allow privilege escalation on its own. Its effect is subtle and data/logic corruption oriented.

MITRE / Weakness Mapping

CWE: CWE-190 — Integer Overflow or Wraparound

This weakness category describes situations where arithmetic operations exceed their maximum representable values and wrap around, causing unexpected results.

Proof-of-Concept (PoC) / Exploitation Availability

At disclosure, no standardized PoC code was broadly published. The maintainers chose to fix the flaw rather than disseminate exploit scripts. However, the conditions that trigger the issue are well understood, and a simple fuzzing or boundary test targeting the three affected functions with numeric limits can reproduce the effects.

Educational PoC Approach

You can create small test contracts or unit tests that:

  1. Call Bytes::slice with a start of 0 and an end value equal to the maximum unsigned integer.
  2. Call Vec::slice with similar extreme bound values.
  3. Call Prng::gen_range::<u64> with an upper bound of zero or lower bound near the maximum.

If compiled without overflow checks, these tests will produce unexpected values or wraparound behavior, demonstrating the existence of the issue.

Remember — this PoC is for educational testing and controlled environments only.

How to Detect Vulnerable Usage

1. Dependency Analysis

Scan your project dependencies for rs-soroban-sdk. If your project directly or indirectly uses an affected version, it is potentially impacted unless compiled with overflow checks.

Example version ranges requiring attention:

  • Versions <= 22.0.8
  • Versions >= 23.0.0 && <= 23.5.0
  • Versions >= 25.0.0 && <= 25.0.1

If the SDK version predates one of the patched releases listed above, upgrade.

2. Build Profile Inspection

Check your Rust build profiles:

Open your Cargo.toml and look for:

[profile.release]
overflow-checks = true

If this line is missing or set to false, the release build will not trap on integer overflow, making the contract susceptible to the silent wrap behavior.

3. Log Monitoring for Unexpected Host Errors

While the silent wrap behavior itself may not always produce a visible error, in some cases the Soroban host will trap when handling out-of-bounds ranges. These show up as host errors tied to invalid object ranges.

To detect this dynamically:

  • Monitor host logs and transaction receipts for error messages related to index bounds or object range violations.
  • Flag spikes in such errors originating from specific contracts after deployment.

Tracking these symptoms over time helps identify contracts misbehaving due to corrupted inputs.

4. Functional Test Cases

Add contract tests that deliberately supply extreme boundary values to all functions that touch:

  • Byte/vector slicing
  • Random number generation ranges

If the contract returns incorrect data slices or unexpected randomness, the underlying library is likely mishandling arithmetic.

Detection Rules

A. CI / Build Rule

Fail build if a vulnerable soroban-sdk version appears in the dependency tree:

cargo metadata --format-version 1 | jq -r '.packages[] |
  select(.name=="soroban-sdk") | .version' | grep -E \
'^22\.0\.[0-8]$|^23\.[0-4]\.|^23\.5\.0$|^25\.0\.0$|^25\.0\.1$' && \
echo "VULNERABLE soroban-sdk detected — upgrade required" && exit 1

This rule blocks merges introducing vulnerable versions.

B. Runtime Log Detection (SIEM)

Create an alert rule that matches Soroban host runtime error patterns showing out-of-bounds range incidents:

index=host_logs "HostError: Error(Object, IndexBounds)" 
| stats count by contract_id, node
| where count > 10

This alerts if a contract repeatedly triggers indexing errors that may stem from wrapped ranges.

C. Grep / Static Pattern Matching

Scan your source for direct calls to risky functions:

grep -R "Bytes::slice" -n src
grep -R "Vec::slice" -n src
grep -R "Prng::gen_range" -n src

Review each match for user-controlled inputs leading into these calls without proper bound validation.

Mitigation & Remediation

1. Upgrade the SDK

Update rs-soroban-sdk to one of the patched versions:

  • Version 25.0.2 or later
  • Version 23.5.1 or later
  • Version 22.0.9 or later

Official patch links:

Upgrading ensures that the underlying arithmetic uses checked_add / checked_sub and no silent wraparound occurs.

2. Enable Overflow Checks

If you cannot upgrade immediately, modify your build profile:

[profile.release]
overflow-checks = true

This forces runtime traps instead of silent wraparound, eliminating the silent corruption vector.

3. Validate Inputs Before Use

Do not pass unvalidated user-derived bounds into slicing or random-range functions. Validate numeric ranges early and return explicit errors if the number is outside expected bounds.

4. Add Targeted Tests

Include unit and integration tests that stress boundaries, such as:

  • Slice from 0 to maximum values
  • Random range with lower bound near maximum and upper bound near 0

Any surprising results should be flagged and fixed.

Final Takeaways

  • This vulnerability stems from integer overflow / wraparound in range handling functions when overflow checks are disabled.
  • It does not allow arbitrary code execution, but it does silently corrupt contract logic.
  • Detection requires both dependency and build configuration analysis, and dynamic monitoring for range errors post-deployment.
  • The only reliable way to fix it is to upgrade the SDK or enable overflow checking and to validate all numeric bounds in your code.

Aegiron

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