mbedtls/ChangeLog.d/mpi_exp_mod-zero.txt

Bugfix
   * Fix a null pointer dereference when mbedtls_mpi_exp_mod() was called with
     A=0 represented with 0 limbs. Up to and including Mbed TLS 2.26, this bug
     could not be triggered by code that constructed A with one of the
     mbedtls_mpi_read_xxx functions (including in particular TLS code) since
     those always built an mpi object with at least one limb.
     Credit to OSS-Fuzz. Fixes #4641.
Changelog for the fix to mbedtls_mpi_exp_mod(A=0) In Mbed TLS 2.26.0, the bug was hard to trigger, since all methods for parsing a bignum (mbedtls_mpi_read_xxx functions) constructed an mbedtls_mpi object with at least one limb. In the development branch, after the commit "New internal function mbedtls_mpi_resize_clear", this bug could be triggered by a TLS server, by passing invalid custom Diffie-Hellman parameters with G=0 transmitted as a 0-length byte string. Since the behavior change in mbedtls_mpi_read_binary and mbedtls_mpi_read_binary_le (constructing 0 limbs instead of 1 when passed empty input) turned out to have consequences despite being in principle an internal detail, mention it in the changelog. Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com> 2021-06-09 16:55:57 +00:00			`Bugfix`
			`* Fix a null pointer dereference when mbedtls_mpi_exp_mod() was called with`
			`A=0 represented with 0 limbs. Up to and including Mbed TLS 2.26, this bug`
			`could not be triggered by code that constructed A with one of the`
			`mbedtls_mpi_read_xxx functions (including in particular TLS code) since`
			`those always built an mpi object with at least one limb.`
			`Credit to OSS-Fuzz. Fixes #4641.`