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GHSA-c4j9-wr9j-4486

CVE Information

Out-of-bounds Read with libsodium-encrypted Files in Vim < 9.2.0671

Date: 17.06.2026 Severity: Medium CVE: CVE-2026-57452 CWE: Integer Underflow (CWE-191), Out-of-bounds Read (CWE-125)

Summary

When Vim opens a file encrypted with the VimCrypt~04! or VimCrypt~05! method (xchacha20poly1305, requires the +sodium feature) whose body is shorter than a single libsodium secretstream header, an unsigned length calculation underflows and a subsequent decryption call reads far past the end of the input buffer, crashing Vim.

Description

crypt_get_header_len() validates only the size of the file header (magic, salt and seed), not the length of the encrypted body that follows. A file with a complete header but a body of 1 to 23 bytes therefore passes the size check. In crypt_sodium_buffer_decode() the secretstream header length is then subtracted from the body length:

    from += crypto_secretstream_xchacha20poly1305_HEADERBYTES;
    len  -= crypto_secretstream_xchacha20poly1305_HEADERBYTES;

len is a size_t, so when the body is shorter than HEADERBYTES the subtraction wraps around to a value close to the maximum. The wrapped length is then passed to crypto_secretstream_xchacha20poly1305_pull(), which reads that many bytes from the input buffer. Because the output buffer was already allocated using the original (small) body length, the corrupted length widens the read rather than a write, resulting in an out-of-bounds read and a crash.

Impact

An attacker who can get a victim to open a crafted, ostensibly encrypted file and enter any key at the prompt can reliably crash Vim (denial of service). No information is disclosed: the decryption call faults on the over-read and never returns plaintext, and the message authentication would fail in any case. Exploitation requires the +sodium feature, user interaction to open the file and supply a key, and is limited to a crash.

Acknowledgements

The Vim project would like to thank Cipher / Causal Security (https://causalsecurity.com/) for reporting and analyzing the issue and suggesting a fix.

References

The issue has been fixed as of Vim patch v9.2.0671. - Commit - Github Security Advisory