{"id":"CVE-2026-59880","aliases":["GHSA-xvcm-6775-5m9r"],"title":"Immutabl: Hash-collision algorithmic complexity denial of service in Immutable.Map/Set","summary":"Immutabl: Hash-collision algorithmic complexity denial of service in Immutable.Map/Set","severity":"high","cwe":["CWE-400","CWE-407"],"vendor":"immutable","product":"immutable","ecosystem":"npm","affected":["immutable < 4.3.9","immutable >= 5.0.0-beta.1, < 5.1.8"],"patched":["immutable 4.3.9","immutable 5.1.8"],"published":"2026-07-21","updated":"2026-07-21","source":"GHSA","sourceUrl":"https://github.com/advisories/GHSA-xvcm-6775-5m9r","references":[{"url":"https://github.com/immutable-js/immutable-js/security/advisories/GHSA-xvcm-6775-5m9r"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-59880"},{"url":"https://github.com/immutable-js/immutable-js/commit/3dd7e5655012597a41873e328bf9142a8901527b"},{"url":"https://github.com/immutable-js/immutable-js/commit/e51d49fc612ded5ec4dfb94ff294d22074269b0f"},{"url":"https://github.com/immutable-js/immutable-js/releases/tag/v4.3.9"},{"url":"https://github.com/immutable-js/immutable-js/releases/tag/v5.1.8"},{"url":"https://github.com/advisories/GHSA-xvcm-6775-5m9r"}],"tags":["ghsa","npm"],"epss":0.00568,"epssPercentile":0.45813,"ingestedAt":"2026-07-21T19:53:40.243Z","slug":"CVE-2026-59880","body":"## Overview\n\n## Summary\n\n`Immutable.Map` and `Immutable.Set` keep keys that share the same 32-bit hash in a collision bucket that is scanned linearly. The string hash is public and deterministic, so an attacker who controls the **keys** inserted into a Map can craft many keys that all collide, degrading insertion and lookup from amortized O(1) to O(n) per operation — and O(n²) to build or read the whole set. A small, attacker-shaped payload can therefore consume disproportionate CPU and, on a single-threaded runtime such as Node.js, stall the event loop and deny service.\n\n## Details\n\nThe string hash uses the JVM-style polynomial `hashed = (31 * hashed + charCode) | 0`. Strings such as `\"Aa\"` and `\"BB\"` hash to the same value (`65*31+97 == 66*31+66 == 2112`), and concatenating such blocks yields `2^n` distinct strings sharing one hash (40 characters ⇒ >1,000,000 colliding keys). \nAll such keys route to a single `HashCollisionNode`, whose `get`/`update` walk the entire bucket testing `is()`. There is no per-process salt, so the colliding set is fully precomputable from the open-source algorithm.\n\n## Proof of concept\n\nInserting N colliding keys (e.g. via `Immutable.Map(obj)` / `Immutable.fromJS(obj)`) is O(N²). Measured on one machine, ~8,000 colliding\nkeys take ~0.7 s to build and ~0.6 s to read, scaling ×4 per doubling; ~16,000 keys exceed several seconds.\n\n## Impact\n\nCPU-bound denial of service in applications that ingest attacker-controlled object **keys** into Immutable structures, e.g. `Immutable.Map(req.body)`, `Immutable.fromJS(req.body)`, `state.merge(userObject)` / `mergeDeep(...)`. Applications that only store attacker input as **values** under fixed keys are not affected.\n\n## Affected versions\n\nAll versions through `5.1.7` (the deterministic string hash and linear collision bucket have existed since the 4.x line).\n\n## Patches\n\nFixed in `5.1.8` _(adjust to the actual release)_: large collision buckets are indexed by a per-process **seeded** secondary hash, restoring near-linear behavior for the affected paths. The public `hash()` is unchanged (no breaking change), and `is()` remains the sole authority on key equality.\n\n## Workarounds\n\nBefore passing untrusted data to Immutable.js: cap request body size, limit object key count/length, and reject high-cardinality payloads; avoid building Maps directly from untrusted object keys.\n\n## References\n\n- CWE-407 (Inefficient Algorithmic Complexity), CWE-400 (Uncontrolled Resource Consumption)\n- OWASP API4:2023 (Unrestricted Resource Consumption)\n\n## Affected packages\n\n- `immutable < 4.3.9`\n- `immutable >= 5.0.0-beta.1, < 5.1.8`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `immutable 4.3.9`\n- `immutable 5.1.8`","depth":"twilight","depthScore":41,"depthScoreParts":{"impact":41.3,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}