Incorrect bounds calculations in substr_compare could lead to an out-of-bounds read when the second string argument passed in is longer than the first. This issue affects HHVM versions prior to 4.56.3, all versions between 4.57.0 and 4.80.1, all versions between 4.81.0 and 4.93.1, and versions 4.94.0, 4.95.0, 4.96.0, 4.97.0, 4.98.0.
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
IntegrityNone
AvailabilityNone
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 | 0.0 → 4.6 |
| 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 | < 4.56.3 |
| facebook | hhvm | < 4.56.3 |
| facebook | hhvm | ≥ 4.57.0, < 4.80.2 |
| facebook | hhvm | ≥ 4.81.0, < 4.93.2 |
| Facebook | HHVM | 4.56.3 |
| Facebook | HHVM | 4.57.0 |
| Facebook | HHVM | 4.80.2 |
| Facebook | HHVM | 4.81.0 |
| Facebook | HHVM | 4.93.2 |
| facebook | hhvm | 4.94.0 |
| Facebook | HHVM | 4.94.0 |
| Facebook | HHVM | 4.94.1 |
| facebook | hhvm | 4.95.0 |
| Facebook | HHVM | 4.95.0 |
| Facebook | HHVM | 4.95.1 |
| facebook | hhvm | 4.96.0 |
| Facebook | HHVM | 4.96.0 |
| Facebook | HHVM | 4.96.1 |
| facebook | hhvm | 4.97.0 |
| Facebook | HHVM | 4.97.0 |
| Facebook | HHVM | 4.97.1 |
| Facebook | HHVM | 4.98.0 |
| facebook | hhvm | 4.98.0 |
| Facebook | HHVM | 4.98.1 |
Published: 2021-03-10
