Unauthenticated code execution via stale BDAT callback
Published May 12, 2026 · Updated May 12, 2026
Use-after-free in Exim 4.97 through 4.99.2 allows remote attackers to execute arbitrary code through a crafted SMTP CHUNKING transfer. During GnuTLS shutdown, tls_close frees xfer_buffer but leaves BDAT's lwr_receive_ungetc callback pointing to tls_ungetc, which writes a newline into the freed buffer after a cleartext tail byte. Exploitation requires an unauthenticated SMTP connection to a GnuTLS build advertising STARTTLS and CHUNKING and can corrupt heap allocator metadata for code execution.
Summary
What happened
Use-after-free in Exim 4.97 through 4.99.2 allows remote attackers to execute arbitrary code through a crafted SMTP CHUNKING transfer. During GnuTLS shutdown, tls_close frees xfer_buffer but leaves BDAT's lwr_receive_ungetc callback pointing to tls_ungetc, which writes a newline into the freed buffer after a cleartext tail byte. Exploitation requires an unauthenticated SMTP connection to a GnuTLS build advertising STARTTLS and CHUNKING and can corrupt heap allocator metadata for code execution.
The record
- CVE
- CVE-2026-45185
- Published
- May 12, 2026
- Updated
- May 12, 2026
- Vendor
- LibSPF2 Project
- Product
- Exim
- Classifications
- CWE-416, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- May 12, 2026CVE publishedPublication date reported by the CVE source.
- May 12, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=4.97 <4.99.3
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
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Public exploit references
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Technologies
Your stack
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Your stack
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