CVE-2024-24561: Vyper's bounds check on built-in `slice()` function can be overflowed

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.9%, percentile 59: FIRST’s model estimates a 0.9% chance of exploitation activity in the next 30 days, higher than 59% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes vyper (PyPI) <= 0.3.10, fixed in 0.4.0. Check your lockfile, including transitive dependencies.

What it is

Vyper is a pythonic Smart Contract Language for the ethereum virtual machine. In versions 0.3.10 and earlier, the bounds check for slices does not account for the ability for start + length to overflow when the values aren't literals. If a slice() function uses a non-literal argument for the start or length variable, this creates the ability for an attacker to overflow the bounds check. This issue can be used to do OOB access to storage, memory or calldata addresses. It can also be used to corrupt the length slot of the respective array.

From the GitHub advisory

Summary

The bounds check for slices does not account for the ability for start + length to overflow when the values aren't literals.

If a slice() function uses a non-literal argument for the start or length variable, this creates the ability for an attacker to overflow the bounds check.

This issue can be used to do OOB access to storage, memory or calldata addresses. It can also be used to corrupt the length slot of the respective array.

A contract search was performed and no vulnerable contracts were found in production.

Weakness type: CWE-119.

Product: vyper (PyPI) · Assigned by: GitHub_M · Published: 2024-02-01

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.90% probability of exploitation activity in the next 30 days; percentile 59.

Timeline

• 2024-02-01 — CVE record published by GitHub_M
• 2024-02-01 — GitHub-reviewed advisory GHSA-9x7f-gwxq-6f2c published (critical)
• 2025-06-17 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-9x7f-gwxq-6f2c github.com
2. CVE.org record CVE-2024-24561 cve.org
3. NVD entry CVE-2024-24561 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com
4. github.com github.com

Critical PyPI advisories · Today’s Security Digest