SMTP send heap buffer overflow
curl might overflow a heap based memory buffer when sending data over SMTP and using a reduced read buffer. When sending data over SMTP, curl allocates a separate "scratch area" on the heap to be able to escape the uploaded data properly if the uploaded data contains data that requires it. The size of this temporary scratch area was mistakenly made to be `2 * sizeof(download_buffer)` when it should have been made `2 * sizeof(upload_buffer)`. The upload and the download buffer sizes are identically sized by default (16KB) but since version 7.54.1, curl can resize the download buffer into a smaller buffer (as well as larger). If the download buffer size is set to a value smaller than 10923, the `Curl_smtp_escape_eob()` function might overflow the scratch buffer when sending contents of sufficient size and contents. The curl command line tool lowers the buffer size when `--limit-rate` is set to a value smaller than 16KB.
02 / AFFECTED SOFTWARE
Affected packages
9 explicit affected versions
18 explicit affected versions
03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
Curl_smtp_escape_eob in lib/smtp.c in curl 7.54.1 to and including curl 7.60.0 has a heap-based buffer overflow that might be exploitable by an attacker who can control the data that curl transmits over SMTP with certain settings (i.e., use of a nonstandard --limit-rate argument or CURLOPT_BUFFERSIZE value).
curl might overflow a heap based memory buffer when sending data over SMTP and using a reduced read buffer. When sending data over SMTP, curl allocates a separate "scratch area" on the heap to be able to escape the uploaded data properly if the uploaded data contains data that requires it. The size of this temporary scratch area was mistakenly made to be `2 * sizeof(download_buffer)` when it should have been made `2 * sizeof(upload_buffer)`. The upload and the download buffer sizes are identically sized by default (16KB) but since version 7.54.1, curl can resize the download buffer into a smaller buffer (as well as larger). If the download buffer size is set to a value smaller than 10923, the `Curl_smtp_escape_eob()` function might overflow the scratch buffer when sending contents of sufficient size and contents. The curl command line tool lowers the buffer size when `--limit-rate` is set to a value smaller than 16KB.
05 / REFERENCES