CVE-2026-124959: Memory Corruption (CVSS 7.1)

Description

The loadIndex function in nmslib hnswlib and Spotify Voyager does not verify that the element count in a serialized HNSW index is within the stored capacity used to allocate the heap buffer. An attacker can supply a crafted index file with an element count greater than the stored capacity, causing the loader to write beyond the allocated buffer and potentially crash the application when it loads the file.

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CVSS v3.1 Score

7.1

HIGH

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

EPSS — Exploit Prediction

0.0017

Probability of exploitation

0.06%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-787 Out-of-bounds Write

References

Other References

https://github.com/nmslib/hnswlib https://github.com/spotify/voyager https://m00dy.sh/notes/when-an-hnsw-index-lies-about-its-capacity

Frequently Asked Questions

What is CVE-2026-124959? +

The loadIndex function in nmslib hnswlib and Spotify Voyager does not verify that the element count in a serialized HNSW index is within the stored capacity used to allocate the heap buffer. An attacker can supply a crafted index file with an element count greater than the stored capacity, causing the loader to write beyond the allocated buffer and potentially crash the application when it loads the file. It has a CVSS v3.1 base score of 7.1 (HIGH).

How severe is CVE-2026-124959? +

CVE-2026-124959 has a CVSS v3.1 score of 7.1 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0017, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-124959? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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