When UpdateRegExpStatics attempted to access initialStringHeap it could already have been garbage collected prior to entering the function, which could potentially have led to an exploitable crash. This vulnerability affects Firefox < 117, Firefox ESR < 115.2, and Thunderbird < 115.2.

References

• https://nvd.nist.gov/vuln/detail/CVE-2023-4577
• https://bugzilla.mozilla.org/show_bug.cgi?id=1847397
• https://www.mozilla.org/security/advisories/mfsa2023-34
• https://www.mozilla.org/security/advisories/mfsa2023-36
• https://www.mozilla.org/security/advisories/mfsa2023-38