{"id":"CVE-2026-65630","kind":"vulnerability","aliases":["CVE-2026-65630"],"related":[],"title":"jose (Erlang): timing leak in X25519 fallback can expose private key","description":"Observable Timing Discrepancy vulnerability in potatosalad jose allows recovery of a long-term X25519 private key through a timing side channel in the pure-Erlang Curve25519 fallback.\n\nThe pure-Erlang X25519 implementation performs scalar multiplication over the secret private key using a recursive Montgomery ladder (jose_jwa_x25519:curve25519/2) whose clauses branch on individual bits of the clamped private scalar, and whose per-step operations (jose_jwa_x25519:montgomery_add/3 and jose_jwa_x25519:montgomery_double/1) and field inversion are built from value-dependent Erlang bignum arithmetic (multiplication, remainder, and modular exponentiation). Although the ladder is operation-count balanced and fixed at 254 steps, the concrete integer values processed at each step, and therefore the running time, depend on the secret scalar. The execution time of the public entry points jose_jwa_x25519:scalarmult/2, jose_jwa_x25519:x25519/2, jose_jwa_x25519:x25519_base/1, and jose_jwa_x25519:sk_to_pk/1 is thus a function of the private key.\n\nThis path is reachable from the public API, most notably when a service decrypts attacker-supplied ECDH-ES (JWE) messages with a long-term X25519 key (for example through JOSE.JWK.box_decrypt_ecdh_es/2, which reaches jose_jwa_curve25519:x25519_shared_secret/2 and the ladder). An attacker who can submit ciphertexts and measure decryption timing can, in principle, recover the private key bit by bit, defeating the resistance X25519 was designed to provide. Recovery of the key compromises the confidentiality and authenticity of all data protected by it.\n\nThis issue affects jose: from 1.10.0 before 1.11.13.","summary":"The pure-Erlang X25519 fallback in the jose library runs time that depends on the secret scalar, so the running time leaks the private key bit by bit. An attacker who can submit ECDH-ES JWE ciphertexts to a service decrypting with a long-term X25519 key and measure timing could in principle recover that key.","severity":"medium","cvss":5.9,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["ecdh-es","elixir","erlang","jose","jwe","package","x25519"],"not_affected_if":["default-config","no-attacker-submitted-ciphertexts"],"how_to_check":"- Check the installed jose version in the project's Erlang/Elixir dependencies (for example `rebar.lock` or `mix.lock`) and see whether it is `1.10.0` or later but before `1.11.13`.\n- Check whether the service calls `JOSE.JWK.box_decrypt_ecdh_es/2` or `jose_jwa_x25519` with a long-term X25519 key.","fix":"- Upgrade jose to `1.11.13` or later.","status":"open","published_at":"2026-10-26T20:17:58+00:00","first_seen_at":"2026-10-26T20:50:18+00:00","triaged_at":"2026-10-26T20:51:47+00:00","updated_at":"2026-10-26T20:51:47+00:00","category":"package","confidence":0.7,"triage":{"at":"2026-10-26T20:51:47Z","model":"claude-haiku-5-5","output":{"fix":"- Upgrade jose to `1.11.13` or later.","reach":"network","title":"jose (Erlang): timing leak in X25519 fallback can expose private key","impact":"high","summary":"The pure-Erlang X25519 fallback in the jose library runs time that depends on the secret scalar, so the running time leaks the private key bit by bit. An attacker who can submit ECDH-ES JWE ciphertexts to a service decrypting with a long-term X25519 key and measure timing could in principle recover that key.","category":"package","nicknames":[],"who_cares":["erlang","elixir","jose","jwe","ecdh-es","x25519"],"confidence":0.7,"needs_auth":"unknown","worst_case":"Long-term X25519 private key recovered via timing, compromising protected data","analyst_note":"Check the NVD entry and the jose release notes for whether the fix covers all X25519 paths and whether the native (NIF) backend is unaffected.","how_to_check":"- Check the installed jose version in the project's Erlang/Elixir dependencies (for example `rebar.lock` or `mix.lock`) and see whether it is `1.10.0` or later but before `1.11.13`.\n- Check whether the service calls `JOSE.JWK.box_decrypt_ecdh_es/2` or `jose_jwa_x25519` with a long-term X25519 key.","needs_analyst":true,"not_affected_if":["default-config","no-attacker-submitted-ciphertexts"],"who_is_affected":"Services that use the jose library from 1.10.0 up to but not including 1.11.13 and decrypt attacker-supplied ECDH-ES JWE messages with a long-term X25519 key, where the pure-Erlang fallback is used. Systems that only sign, only use other key types, or never receive attacker-controlled ciphertexts are unlikely to be exposed.","user_interaction":"no","needs_special_setup":"unknown","severity_if_unknown":"medium"},"cost_usd":0.000723,"input_tokens":3848,"output_tokens":677,"severity_before":"medium"},"analyst_status":null,"analyst_note":null,"search":"'-2026':13A,16A '-65630':14A,17A '1.10.0':345C '1.11.13':347C '254':194C 'add/3':159C 'affect':342C 'allow':93C 'although':183C 'api':257C 'arithmet':177C 'attack':57B,265C,298C 'attacker-suppli':264C 'authent':333C 'balanc':190C 'base/1':234C 'bignum':176C 'bit':53B,55B,143C,314C,316C 'branch':140C 'built':170C 'channel':107C 'ciphertext':65B,302C 'clamp':146C 'claus':139C 'compromis':329C 'concret':197C 'confidenti':331C 'could':80B 'count':189C 'curve25519':113C,290C 'curve25519/2':137C 'cve':12A,15A 'data':336C 'decrypt':69B,263C,283C,305C 'defeat':317C 'depend':40B,174C,209C 'design':322C 'discrep':88C 'double/1':165C 'ecdh':19B,62B,268C,284C 'ecdh-':18B,61B,267C 'elixir':21B 'entri':220C 'erlang':2A,22B,30B,112C,118C,175C 'es':20B,63B,269C 'es/2':285C 'exampl':280C 'execut':215C 'exponenti':182C 'expos':9A 'fallback':7A,32B,114C 'field':167C 'fix':192C 'function':245C 'implement':120C 'individu':142C 'integ':198C 'invers':168C 'issu':341C 'jose':1A,23B,35B,92C,134C,155C,161C,222C,226C,230C,236C,288C,343C 'jose.jwk.box':282C 'jwa':135C,156C,162C,223C,227C,231C,237C,289C 'jwe':24B,64B,270C 'key':11A,52B,76B,85B,102C,128C,249C,278C,313C,328C 'ladder':133C,185C,296C 'leak':4A,49B 'librari':36B 'long':73B,98C,275C 'long-term':72B,97C,274C 'measur':78B,304C 'messag':271C 'modular':181C 'montgomeri':132C,158C,164C 'multipl':123C,178C 'notabl':259C 'observ':86C 'oper':154C,188C 'operation-count':187C 'packag':25B 'path':251C 'per':152C 'per-step':151C 'perform':121C 'pk/1':241C 'point':221C 'potatosalad':91C 'principl':82B,309C 'privat':10A,51B,101C,127C,147C,248C,312C 'process':200C 'protect':337C 'provid':324C 'public':219C,256C 'pure':29B,111C,117C 'pure-erlang':28B,110C,116C 'reach':287C 'reachabl':253C 'recov':83B,310C 'recoveri':94C,325C 'recurs':131C 'remaind':179C 'resist':319C 'run':37B,47B,207C 'scalar':44B,122C,148C,213C 'scalarmult/2':225C 'secret':43B,126C,212C 'secret/2':293C 'servic':68B,262C 'share':292C 'side':106C 'sk':239C 'step':153C,195C,203C 'submit':60B,301C 'suppli':266C 'term':74B,99C,276C 'therefor':205C 'thus':243C 'time':3A,38B,48B,79B,87C,105C,208C,216C,306C 'use':129C 'valu':173C,199C 'value-depend':172C 'vulner':89C 'whose':138C,150C 'x25519':6A,26B,31B,75B,100C,119C,136C,157C,163C,224C,228C,232C,233C,238C,277C,291C,320C 'x25519/2':229C","nicknames":[],"mitigations":[],"who_affected":"Services that use the jose library from 1.10.0 up to but not including 1.11.13 and decrypt attacker-supplied ECDH-ES JWE messages with a long-term X25519 key, where the pure-Erlang fallback is used. Systems that only sign, only use other key types, or never receive attacker-controlled ciphertexts are unlikely to be exposed.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-26T20:17:58+00:00","kev":null,"cvss_vector":"CVSS:4.0/AV:L/AC:H/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","cvss_by":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-65630","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-65630","severity":null,"published_at":"2026-10-26T20:17:58+00:00","modified_at":"2026-10-26T20:17:58+00:00","first_seen_at":"2026-10-26T20:50:18+00:00","fetched_at":"2026-10-26T20:50:18+00:00","note":null}],"documents":[],"notice":"Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai"}