How severe is CVE-2023-23556?

CVE-2023-23556 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2023-23556 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (55th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2023-23556?

CVE-2023-23556 affects Facebook Hermes. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2023-23556?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2023-23556 published?

CVE-2023-23556 was published on 2023-05-18 and last updated on 2026-06-17.

CVE-2023-23556

CVE-2023-23556 is a critical-severity vulnerability in Facebook Hermes with a CVSS 3.x base score of 9.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-787.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
EPSS exploit prediction: 1% (55th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-787
Affected product: Facebook Hermes
Published: 2023-05-18
Last modified: 2026-06-17

Description

An error in BigInt conversion to Number in Hermes prior to commit a6dcafe6ded8e61658b40f5699878cd19a481f80 could have been used by a malicious attacker to execute arbitrary code due to an out-of-bound write. Note that this bug is only exploitable in cases where Hermes is used to execute untrusted JavaScript. Hence, most React Native applications are not affected.

Frequently asked questions

What is CVE-2023-23556?: An error in BigInt conversion to Number in Hermes prior to commit a6dcafe6ded8e61658b40f5699878cd19a481f80 could have been used by a malicious attacker to execute arbitrary code due to an out-of-bound write. Note that this bug is only exploitable in cases where Hermes is used to execute untrusted JavaScript. Hence, most React Native applications are not affected.
How severe is CVE-2023-23556?: CVE-2023-23556 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2023-23556 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (55th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2023-23556?: CVE-2023-23556 affects Facebook Hermes. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2023-23556?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2023-23556 published?: CVE-2023-23556 was published on 2023-05-18 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:facebook:hermes:*:*:*:*:*:*:*:*

More vulnerabilities in Facebook Hermes

CVE-2023-30470 — Critical (CVSS 9.8): A use-after-free related to unsound inference in the bytecode generation when optimizations are enabled for Hermes…
CVE-2023-28081 — Critical (CVSS 9.8): A bytecode optimization bug in Hermes prior to commit e6ed9c1a4b02dc219de1648f44cd808a56171b81 could be used to cause…
CVE-2023-25933 — Critical (CVSS 9.8): A type confusion bug in TypedArray prior to commit e6ed9c1a4b02dc219de1648f44cd808a56171b81 could have been used by a…
CVE-2023-23557 — Critical (CVSS 9.8): An error in Hermes' algorithm for copying objects properties prior to commit a00d237346894c6067a594983be6634f4168c9ad…
CVE-2022-40138 — Critical (CVSS 9.8): An integer conversion error in Hermes bytecode generation, prior to commit 6aa825e480d48127b480b08d13adf70033237097,…
CVE-2022-35289 — Critical (CVSS 9.8): A write-what-where condition in hermes caused by an integer overflow, prior to commit…

All CVEs affecting Facebook Hermes →

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