Hydrolysis of malonic acids under acidic conditions should not be attempted. DImethyl malonates may be hydrolyzed under mild basic conditions to give salts of the respective malonic acids. However, attempts to release the free acids are expected to result primarily in decarboxylation. If your plan is further conversion of malonic acids to e.c. the respective diamides or diols, using dialkyl malonates is a more productive approach.

You can use LiBr, Et3N and MeCN (containing 2 vol % of water) reaction conditions. These conditions allow room temperature hydrolysis to be carried out (15 min - 48h). This is the reference that related to: Article A Mild Hydrolysis of Esters Mediated by Lithium Salts

But I don't know examples of application this method for dialkylmalonate substrates. If you try this, please share the results.

2-Benzylmalonic Acid: 2-Benzyl(ethyl malonate) (5.2 g, 21 mmol) was poured onto pulverized KOH (4.7 g, 94 mmol) in an ice/water bath. The mixture rapidly became highly viscous and ethanol (2 mL) and water (1.3 mL) were added to allow stirring. After 6 h of stirring at 90 °C, the suspension was dissolved in H2O (30 mL) and twice washed with CH2Cl2 (3 × 10 mL) before concentrated HCl was added to reach pH 1. The reaction product was collected by washing with CH2Cl2 (5 × 20 mL). The solution was dried over MgSO4, and evaporation of the solvent afforded 2-benzylmalonic acid (1.7 g, 41%).

also WO2006127576A2 pag. 25 (acidic liquid-liquid extraction)

Article A New Family of Low-Spin CoIII Bis(amidate) Complexes with T...