Integer overflow in libmime buffer growth could lead to heap corruption

Several buffer-growth sites in libmime performed size arithmetic in 32-bit types without overflow checks. On a sufficiently large message the growth guard could fail open, or the buffer could be reallocated smaller than required, and a subsequent memcpy would then write attacker-controlled data across adjacent heap allocations. This vulnerability was fixed in Thunderbird 158 and Thunderbird 153.6.

Source published

13 Oct 2026 18:08:37 UTC

Source modified

27 Oct 2026 18:27:45 UTC

Observed here

27 Oct 2026 19:45:55 UTC

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