In its interim report, HSBC said it had received requests from "various regulatory and law enforcement authorities around the world" for information on Mossack Fonseca & Co, the Panama law firm whose data was leaked earlier this year.
HSBC was a major client of Mossack Fonseca, according to media reports, and has denied wrongdoing. It is alleged that banks and other entities used the law firm to help clients evade taxes.
The investigation into Mossack Fonseca was one of multiple legal proceedings the bank detailed in its results. Others included litigation relating to the Bernie Madoff Ponzi scheme, an investigation into loans sold by the bank to purchase mortgage securitizations before the global financial crisis and investigations into the alleged manipulation of Libor (London Interbank Offered Rate) and alleged non-compliance with anti-money laundering laws.
"Litigation remains a key risk for the banking sector, and HSBC's report on the legal proceedings facing the bank reads like a barely trimmed-down version of 'War and Peace.' This includes a section on the Panama Papers, which states HSBC does not know at present what, if anything, the impact on the bank will be, but warns it could be significant," Laith Khalaf, senior analyst at FTSE 100-listed financial services firm Hargreaves Lansdown, said in a note on Wednesday.
After the results were out, Hong Kong-listed shares of HSBC were down 1.7 percent, unchanged from levels before the release, but HSBC's London-listed shares were up nearly 4 percent in early Wednesday trading on news of the buyback.
Chief executive Stuart Gulliver wrote in a statement that the bank had performed "reasonably well in the first half in the face of considerable uncertainty," and that the reduction in profit reflected what had been a strong first half in 2015.
Investors will closely analyze the bank's outlook following the historic Brexit vote in June, which saw the U.K. vote to exit the European Union (EU).