# CVE-2026-124959: Nmaslib Hnswlib and Spotify Voyager HNSW Index Deserialization Heap Out-of-Bounds Write

Status: published. Published: 2026-11-09. Updated: 2026-11-09.

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.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Spotify / Voyager: ≥ 2.0.7; ≤ 2.1.1 (affected, custom). Source: CNA: certcc
- hnswlib / hnswlib: ≥ 0.5.0; ≤ 0.9.0 (affected, custom). Source: CNA: certcc

## Severity and prioritization

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-787

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://m00dy.sh/notes/when-an-hnsw-index-lies-about-its-capacity (CNA: certcc)

- https://github.com/nmslib/hnswlib (CNA: certcc)

- https://github.com/spotify/voyager (CNA: certcc)

## Provenance

- CNA: certcc: https://www.cve.org/CVERecord?id=CVE-2026-124959; retrieved 2026-11-09; source updated 2026-11-09

Revision: 6b7a0c354b516627deea33750fd289502fb4af43ed9aea8886085de64706dc49

Canonical: https://y2.dev/cve/CVE-2026-124959

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