Many Ethereum nodes running popular clients like Parity and Geth take months to apply security patches, which may leave the network vulnerable to 51% attacks (Security Research Labs)

Security Research Labs:
Many Ethereum nodes running popular clients like Parity and Geth take months to apply security patches, which may leave the network vulnerable to 51% attacks  —  SRLabs research suggests that security vulnerabilities remain unpatched for many Ethereum blockchain participants for extended periods of time …