When unserializing an object with dynamic properties HHVM needs to pre-reserve the full size of the dynamic property array before inserting anything into it. Otherwise the array might resize, invalidating previously stored references. This pre-reservation was not occurring in HHVM prior to v4.32.3, between versions 4.33.0 and 4.56.0, 4.57.0, 4.58.0, 4.58.1, 4.59.0, 4.60.0, 4.61.0, 4.62.0.
An official patch is available. Apply the patch as soon as possible.
CVSS v4.0 Metrics
Exploitability
Attack VectorNetwork
ComplexityLow
RequirementsPresent
PrivilegesNone
User InteractionNone
Threat
Exploit MaturityUnreported
Vulnerable System
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
Subsequent System
ConfidentialityNone
IntegrityNone
AvailabilityNone
Supplemental
SafetyNegligible
AutomatableYes
RecoveryAutomatic
Value DensityConcentrated
UrgencyMedium
Patch StatusOfficial Patch
Change Log
| Date | Source | Changes | Score |
|---|
| 2026-07-21 | nvd | AV: P→N, AC: H→L, PR: H→N, UI: A→N, VC: N→H, VI: N→H, VA: N→H | 0.0 → 7.2 |
| 2026-07-21 | nvd | patch: Unavailable→Official Patch | 0.0 → 0.0 |
| 2026-07-21 | cve.org | initial, patch: Unavailable | 0.0 |
Affected Software
| Vendor | Product | Version |
|---|
| facebook | hhvm | ≥ 4.33.0, < 4.56.1 |
| Facebook | HHVM | < 4.32.3 |
| facebook | hhvm | < 4.32.3 |
| Facebook | HHVM | 4.32.3 |
| Facebook | HHVM | 4.33.0 |
| Facebook | HHVM | 4.56.1 |
| facebook | hhvm | 4.57.0 |
| Facebook | HHVM | 4.57.0 |
| Facebook | HHVM | 4.57.1 |
| facebook | hhvm | 4.58.0 |
| Facebook | HHVM | 4.58.0 |
| facebook | hhvm | 4.58.1 |
| Facebook | HHVM | 4.58.2 |
| Facebook | HHVM | 4.59.0 |
| facebook | hhvm | 4.59.0 |
| Facebook | HHVM | 4.59.1 |
| facebook | hhvm | 4.60.0 |
| Facebook | HHVM | 4.60.0 |
| Facebook | HHVM | 4.60.1 |
| facebook | hhvm | 4.61.0 |
| Facebook | HHVM | 4.61.0 |
| Facebook | HHVM | 4.61.1 |
| Facebook | HHVM | 4.62.0 |
| facebook | hhvm | 4.62.0 |
| Facebook | HHVM | 4.62.1 |
Published: 2021-03-11
