CVE-2026-59880
Immutable.js hash-collision DoS: crafted keys cause excessive CPU on Map/Set operations
Is CVE-2026-59880 being exploited?
Not confirmed. CVE-2026-59880 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.57% probability of exploitation in the next 30 days.
How severe is CVE-2026-59880?
CVE-2026-59880 is rated High. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-59880?
Yes. A fix has been recorded for CVE-2026-59880. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-59880 affect?
CVE-2026-59880 affects Immutable.js < 4.3.9, Immutable.js < 5.1.8, Apps using Immutable.Map(), Immutable.fromJS(), state.merge(), mergeDeep. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-59880?
Upgrade Immutable.js to >=4.3.9 or >=5.1.8; sanitize/limit untrusted keys
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
CPU exhaustion (denial of service) via attacker-controlled colliding keys in Immutable.Map/Set, degrading insertion and lookup performance.
Patch when possible
- affected< 4.3.9
- affected>= 5.0.0-beta.1 and < 5.1.8
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.