PGP (Pretty Good Privacy) is a data encryption method sometimes added to programs that send and receive email.
Details about the vulnerability were released by the Suddeutsche Zeitung newspaper prior to a scheduled embargo.
Previously, the Electronic Frontier Foundation (EFF) had advised immediately disabling email tools that automatically decrypted PGP.
The problem had been investigated by Sebastian Schinzel, at Munster University of Applied Sciences.
After the embargo on releasing details about the vulnerability was lifted, Mr Schinzel and colleagues published their research revealing how the attack on PGP emails worked.
A website explaining the issue has also now been made public.
Mr Schinzel has been contacted by the BBC for comment.
There was initially concern among cyber-security researchers that the issue affected the core protocol of PGP – meaning that all uses of the encryption method, including file encryption, could be made vulnerable.
However, one provider of software that can encrypt data using PGP explained the problem specifically concerned email programs that failed to check for decryption errors properly before following links in emails that included HTML code.
The issue had been “overblown” by the EFF, said Werner Koch, of GnuPG.
His colleague Robert Hansen said on Twitter that the issue had been known about for some time.